diff --git a/plugins/chat/app/controllers/chat/api/thread_reads_controller.rb b/plugins/chat/app/controllers/chat/api/thread_reads_controller.rb
new file mode 100644
index 00000000000..dfb72d9b70f
--- /dev/null
+++ b/plugins/chat/app/controllers/chat/api/thread_reads_controller.rb
@@ -0,0 +1,11 @@
+# frozen_string_literal: true
+
+class Chat::Api::ThreadReadsController < Chat::ApiController
+  def update
+    params.require(%i[channel_id thread_id])
+
+    with_service(Chat::UpdateUserThreadLastRead) do
+      on_model_not_found(:thread) { raise Discourse::NotFound }
+    end
+  end
+end
diff --git a/plugins/chat/app/jobs/regular/chat/notify_mentioned.rb b/plugins/chat/app/jobs/regular/chat/notify_mentioned.rb
index e88798a74c0..3388d17973a 100644
--- a/plugins/chat/app/jobs/regular/chat/notify_mentioned.rb
+++ b/plugins/chat/app/jobs/regular/chat/notify_mentioned.rb
@@ -40,6 +40,8 @@ module Jobs
           is_direct_message_channel: @chat_channel.direct_message_channel?,
         }
 
+        data[:chat_thread_id] = @chat_message.thread_id if @chat_message.in_thread?
+
         if !@is_direct_message_channel
           data[:chat_channel_title] = @chat_channel.title(membership.user)
           data[:chat_channel_slug] = @chat_channel.slug
@@ -61,12 +63,19 @@ module Jobs
       end
 
       def build_payload_for(membership, identifier_type:)
+        post_url =
+          if @chat_message.in_thread?
+            @chat_message.thread.relative_url
+          else
+            "#{@chat_channel.relative_url}/#{@chat_message.id}"
+          end
+
         payload = {
           notification_type: ::Notification.types[:chat_mention],
           username: @creator.username,
           tag: ::Chat::Notifier.push_notification_tag(:mention, @chat_channel.id),
           excerpt: @chat_message.push_notification_excerpt,
-          post_url: "#{@chat_channel.relative_url}/#{@chat_message.id}",
+          post_url: post_url,
         }
 
         translation_prefix =
diff --git a/plugins/chat/app/services/chat/action/mark_mentions_read.rb b/plugins/chat/app/services/chat/action/mark_mentions_read.rb
index 602b227caf1..8d0207d63bb 100644
--- a/plugins/chat/app/services/chat/action/mark_mentions_read.rb
+++ b/plugins/chat/app/services/chat/action/mark_mentions_read.rb
@@ -10,7 +10,9 @@ module Chat
       #   marked as read.
       # @param [Integer] message_id Optional, used to limit the max message ID to mark
       #   mentions read for in the channel.
-      def self.call(user, channel_ids:, message_id: nil)
+      # @param [Integer] thread_id Optional, if provided then all notifications related
+      #   to messages in the thread will be marked as read.
+      def self.call(user, channel_ids:, message_id: nil, thread_id: nil)
         ::Notification
           .where(notification_type: Notification.types[:chat_mention])
           .where(user: user)
@@ -19,8 +21,14 @@ module Chat
           .joins("INNER JOIN chat_messages ON chat_mentions.chat_message_id = chat_messages.id")
           .where("chat_messages.chat_channel_id IN (?)", channel_ids)
           .then do |notifications|
-            break notifications if message_id.blank?
-            notifications.where("chat_messages.id <= ?", message_id)
+            break notifications if message_id.blank? && thread_id.blank?
+            break notifications.where("chat_messages.id <= ?", message_id) if message_id.present?
+            if thread_id.present?
+              notifications.where(
+                "chat_messages.id IN (SELECT id FROM chat_messages WHERE thread_id = ?)",
+                thread_id,
+              )
+            end
           end
           .update_all(read: true)
       end
diff --git a/plugins/chat/app/services/chat/mark_all_user_channels_read.rb b/plugins/chat/app/services/chat/mark_all_user_channels_read.rb
index c3a67338d85..9c6376fbc63 100644
--- a/plugins/chat/app/services/chat/mark_all_user_channels_read.rb
+++ b/plugins/chat/app/services/chat/mark_all_user_channels_read.rb
@@ -49,7 +49,7 @@ module Chat
     def mark_associated_mentions_as_read(guardian:, updated_memberships:, **)
       return if updated_memberships.empty?
 
-      Chat::Action::MarkMentionsRead.call(
+      ::Chat::Action::MarkMentionsRead.call(
         guardian.user,
         channel_ids: updated_memberships.map(&:channel_id),
       )
diff --git a/plugins/chat/app/services/chat/update_user_last_read.rb b/plugins/chat/app/services/chat/update_user_last_read.rb
index 5d2b66e60fb..3ba18cb0d4b 100644
--- a/plugins/chat/app/services/chat/update_user_last_read.rb
+++ b/plugins/chat/app/services/chat/update_user_last_read.rb
@@ -61,7 +61,7 @@ module Chat
     end
 
     def mark_associated_mentions_as_read(active_membership:, contract:, **)
-      Chat::Action::MarkMentionsRead.call(
+      ::Chat::Action::MarkMentionsRead.call(
         active_membership.user,
         channel_ids: [active_membership.chat_channel.id],
         message_id: contract.message_id,
diff --git a/plugins/chat/app/services/chat/update_user_thread_last_read.rb b/plugins/chat/app/services/chat/update_user_thread_last_read.rb
new file mode 100644
index 00000000000..70845090a8d
--- /dev/null
+++ b/plugins/chat/app/services/chat/update_user_thread_last_read.rb
@@ -0,0 +1,61 @@
+# frozen_string_literal: true
+
+module Chat
+  # Service responsible for marking messages in a thread
+  # as read. For now this just marks any mentions in the thread
+  # as read, but as we add user tracking state to threads it
+  # will work in a similar way to Chat::UpdateUserLastRead
+  #
+  # @example
+  #  Chat::UpdateUserThreadLastRead.call(channel_id: 2, thread_id: 3, guardian: guardian)
+  #
+  class UpdateUserThreadLastRead
+    include ::Service::Base
+
+    # @!method call(channel_id:, thread_id:, guardian:)
+    #   @param [Integer] channel_id
+    #   @param [Integer] thread_id
+    #   @param [Guardian] guardian
+    #   @return [Service::Base::Context]
+
+    contract
+    model :thread
+    policy :invalid_access
+    step :mark_associated_mentions_as_read
+    step :publish_new_last_read_to_clients
+
+    # @!visibility private
+    class Contract
+      attribute :thread_id, :integer
+      attribute :channel_id, :integer
+
+      validates :thread_id, :channel_id, presence: true
+    end
+
+    private
+
+    def fetch_thread(contract:, **)
+      ::Chat::Thread.find_by(id: contract.thread_id, channel_id: contract.channel_id)
+    end
+
+    def invalid_access(guardian:, thread:, **)
+      guardian.can_join_chat_channel?(thread.channel)
+    end
+
+    def mark_associated_mentions_as_read(thread:, guardian:, **)
+      ::Chat::Action::MarkMentionsRead.call(
+        guardian.user,
+        channel_ids: [thread.channel_id],
+        thread_id: thread.id,
+      )
+    end
+
+    def publish_new_last_read_to_clients(guardian:, thread:, **)
+      ::Chat::Publisher.publish_user_tracking_state(
+        guardian.user,
+        thread.channel_id,
+        thread.replies.last.id,
+      )
+    end
+  end
+end
diff --git a/plugins/chat/assets/javascripts/discourse/components/chat-thread.js b/plugins/chat/assets/javascripts/discourse/components/chat-thread.js
index 90993d746eb..baf84060e22 100644
--- a/plugins/chat/assets/javascripts/discourse/components/chat-thread.js
+++ b/plugins/chat/assets/javascripts/discourse/components/chat-thread.js
@@ -1,4 +1,5 @@
 import Component from "@glimmer/component";
+import { Promise } from "rsvp";
 import { tracked } from "@glimmer/tracking";
 import { action } from "@ember/object";
 import ChatMessage from "discourse/plugins/chat/discourse/models/chat-message";
@@ -93,7 +94,7 @@ export default class ChatThreadPanel extends Component {
   @debounce(100)
   fetchMessages() {
     if (this._selfDeleted) {
-      return;
+      return Promise.resolve();
     }
 
     this.loadingMorePast = true;
@@ -138,6 +139,8 @@ export default class ChatThreadPanel extends Component {
         // } else if (messages.length) {
         //   this.scrollToMessage(messages.lastObject.id);
         // }
+        //
+        this.markThreadAsRead();
       })
       .catch(this.#handleErrors)
       .finally(() => {
@@ -179,6 +182,13 @@ export default class ChatThreadPanel extends Component {
     return [messages, results.meta];
   }
 
+  // NOTE: At some point we want to do this based on visible messages
+  // and scrolling; for now it's enough to do it when the thread panel
+  // opens/messages are loaded since we have no pagination for threads.
+  markThreadAsRead() {
+    return this.chatApi.markThreadAsRead(this.channel.id, this.thread.id);
+  }
+
   @action
   onSendMessage(message) {
     if (message.editing) {
diff --git a/plugins/chat/assets/javascripts/discourse/initializers/chat-user-menu.js b/plugins/chat/assets/javascripts/discourse/initializers/chat-user-menu.js
index ca30056fcda..b2c0d4ca8c5 100644
--- a/plugins/chat/assets/javascripts/discourse/initializers/chat-user-menu.js
+++ b/plugins/chat/assets/javascripts/discourse/initializers/chat-user-menu.js
@@ -59,9 +59,16 @@ export default {
                   title: this.notification.data.chat_channel_title,
                   slug: this.notification.data.chat_channel_slug,
                 });
-                return `/chat/c/${slug || "-"}/${
+
+                let notificationRoute = `/chat/c/${slug || "-"}/${
                   this.notification.data.chat_channel_id
-                }/${this.notification.data.chat_message_id}`;
+                }`;
+                if (this.notification.data.chat_thread_id) {
+                  notificationRoute += `/t/${this.notification.data.chat_thread_id}`;
+                } else {
+                  notificationRoute += `/${this.notification.data.chat_message_id}`;
+                }
+                return notificationRoute;
               }
 
               get linkTitle() {
diff --git a/plugins/chat/assets/javascripts/discourse/models/chat-channel.js b/plugins/chat/assets/javascripts/discourse/models/chat-channel.js
index 76ba2a1209b..8bdc0d26180 100644
--- a/plugins/chat/assets/javascripts/discourse/models/chat-channel.js
+++ b/plugins/chat/assets/javascripts/discourse/models/chat-channel.js
@@ -202,8 +202,8 @@ export default class ChatChannel extends RestModel {
       return;
     }
 
-    // TODO (martin) Change this to use chatApi service once we change this
-    // class not to use RestModel
+    // TODO (martin) Change this to use chatApi service markChannelAsRead once we change this
+    // class not to use RestModel.
     return ajax(`/chat/api/channels/${this.id}/read/${messageId}`, {
       method: "PUT",
     });
diff --git a/plugins/chat/assets/javascripts/discourse/services/chat-api.js b/plugins/chat/assets/javascripts/discourse/services/chat-api.js
index 3c29d8041f3..d28d92663fc 100644
--- a/plugins/chat/assets/javascripts/discourse/services/chat-api.js
+++ b/plugins/chat/assets/javascripts/discourse/services/chat-api.js
@@ -407,6 +407,20 @@ export default class ChatApi extends Service {
     return this.#putRequest(`/channels/${channelId}/read/${messageId}`);
   }
 
+  /**
+   * Marks all messages and mentions in a thread as read. This is quite
+   * far-reaching for now, and is not granular since there is no membership/
+   * read state per-user for threads. In future this will be expanded to
+   * also pass message ID in the same way as markChannelAsRead
+   *
+   * @param {number} channelId - The ID of the channel for the thread being marked as read.
+   * @param {number} threadId - The ID of the thread being marked as read.
+   * @returns {Promise}
+   */
+  markThreadAsRead(channelId, threadId) {
+    return this.#putRequest(`/channels/${channelId}/threads/${threadId}/read`);
+  }
+
   get #basePath() {
     return "/chat/api";
   }
diff --git a/plugins/chat/assets/javascripts/discourse/widgets/chat-mention-notification-item.js b/plugins/chat/assets/javascripts/discourse/widgets/chat-mention-notification-item.js
index beeeb4c34f4..6b64fe8ed9e 100644
--- a/plugins/chat/assets/javascripts/discourse/widgets/chat-mention-notification-item.js
+++ b/plugins/chat/assets/javascripts/discourse/widgets/chat-mention-notification-item.js
@@ -48,9 +48,15 @@ const chatNotificationItem = {
       title: data.chat_channel_title,
       slug: data.chat_channel_slug,
     });
-    return `/chat/c/${slug || "-"}/${data.chat_channel_id}/${
-      data.chat_message_id
-    }`;
+
+    let notificationRoute = `/chat/c/${slug || "-"}/${data.chat_channel_id}`;
+    if (data.chat_thread_id) {
+      notificationRoute += `/t/${data.chat_thread_id}`;
+    } else {
+      notificationRoute += `/${data.chat_message_id}`;
+    }
+
+    return notificationRoute;
   },
 };
 
diff --git a/plugins/chat/config/routes.rb b/plugins/chat/config/routes.rb
index 53d1a723fb6..594f23f2b3c 100644
--- a/plugins/chat/config/routes.rb
+++ b/plugins/chat/config/routes.rb
@@ -29,6 +29,7 @@ Chat::Engine.routes.draw do
     get "/mentions/groups" => "hints#check_group_mentions", :format => :json
 
     get "/channels/:channel_id/threads/:thread_id" => "channel_threads#show"
+    put "/channels/:channel_id/threads/:thread_id/read" => "thread_reads#update"
 
     put "/channels/:channel_id/messages/:message_id/restore" => "channel_messages#restore"
     delete "/channels/:channel_id/messages/:message_id" => "channel_messages#destroy"
diff --git a/plugins/chat/spec/jobs/regular/chat/notify_mentioned_spec.rb b/plugins/chat/spec/jobs/regular/chat/notify_mentioned_spec.rb
index a72aa02b4bd..7ac9d674613 100644
--- a/plugins/chat/spec/jobs/regular/chat/notify_mentioned_spec.rb
+++ b/plugins/chat/spec/jobs/regular/chat/notify_mentioned_spec.rb
@@ -21,9 +21,20 @@ describe Jobs::Chat::NotifyMentioned do
     end
   end
 
-  def create_chat_message(channel: public_channel, author: user_1, mentioned_user: user_2)
+  def create_chat_message(
+    channel: public_channel,
+    author: user_1,
+    mentioned_user: user_2,
+    thread: nil
+  )
     message =
-      Fabricate(:chat_message, chat_channel: channel, user: author, created_at: 10.minutes.ago)
+      Fabricate(
+        :chat_message,
+        chat_channel: channel,
+        user: author,
+        created_at: 10.minutes.ago,
+        thread: thread,
+      )
     Fabricate(:chat_mention, chat_message: message, user: mentioned_user)
     message
   end
@@ -408,6 +419,29 @@ describe Jobs::Chat::NotifyMentioned do
         expect(desktop_notification.data[:translated_title]).to eq(payload_translated_title)
       end
 
+      context "when the mention is within a thread" do
+        before do
+          SiteSetting.enable_experimental_chat_threaded_discussions = true
+          public_channel.update!(threading_enabled: true)
+        end
+
+        fab!(:thread) { Fabricate(:chat_thread, channel: public_channel) }
+
+        it "uses the thread URL for the post_url in the desktop notification" do
+          message = create_chat_message(thread: thread)
+          desktop_notification =
+            track_desktop_notification(message: message, to_notify_ids_map: to_notify_ids_map)
+          expect(desktop_notification.data[:post_url]).to eq(thread.relative_url)
+        end
+
+        it "includes the thread ID in the core notification data" do
+          message = create_chat_message(thread: thread)
+          created_notification =
+            track_core_notification(message: message, to_notify_ids_map: to_notify_ids_map)
+          expect(created_notification.data_hash[:chat_thread_id]).to eq(thread.id)
+        end
+      end
+
       context "with private channels" do
         it "users a different translated title" do
           message = create_chat_message(channel: @personal_chat_channel)
diff --git a/plugins/chat/spec/requests/chat/api/thread_reads_controller_spec.rb b/plugins/chat/spec/requests/chat/api/thread_reads_controller_spec.rb
new file mode 100644
index 00000000000..4f1c0808c33
--- /dev/null
+++ b/plugins/chat/spec/requests/chat/api/thread_reads_controller_spec.rb
@@ -0,0 +1,72 @@
+# frozen_string_literal: true
+
+RSpec.describe Chat::Api::ThreadReadsController do
+  fab!(:current_user) { Fabricate(:user) }
+
+  before do
+    SiteSetting.chat_enabled = true
+    SiteSetting.chat_allowed_groups = Group::AUTO_GROUPS[:everyone]
+    sign_in(current_user)
+  end
+
+  describe "#update" do
+    describe "marking the thread messages as read" do
+      fab!(:channel) { Fabricate(:chat_channel) }
+      fab!(:other_user) { Fabricate(:user) }
+      fab!(:thread) { Fabricate(:chat_thread, channel: channel) }
+      fab!(:message_1) do
+        Fabricate(:chat_message, chat_channel: channel, user: other_user, thread: thread)
+      end
+      fab!(:message_2) do
+        Fabricate(:chat_message, chat_channel: channel, user: other_user, thread: thread)
+      end
+
+      context "when the user cannot access the channel" do
+        fab!(:channel) { Fabricate(:private_category_channel) }
+        fab!(:thread) { Fabricate(:chat_thread, channel: channel) }
+        it "raises invalid access" do
+          put "/chat/api/channels/#{channel.id}/threads/#{thread.id}/read.json"
+          expect(response.status).to eq(403)
+        end
+      end
+
+      context "when the channel_id and thread_id params do not match" do
+        it "raises a not found" do
+          put "/chat/api/channels/#{Fabricate(:chat_channel).id}/threads/#{thread.id}/read.json"
+          expect(response.status).to eq(404)
+        end
+      end
+
+      it "marks all mention notifications as read for the thread" do
+        notification_1 = create_notification_and_mention_for(current_user, other_user, message_1)
+        notification_2 = create_notification_and_mention_for(current_user, other_user, message_2)
+
+        put "/chat/api/channels/#{channel.id}/threads/#{thread.id}/read.json"
+        expect(response.status).to eq(200)
+        expect(notification_1.reload.read).to eq(true)
+        expect(notification_2.reload.read).to eq(true)
+      end
+    end
+  end
+
+  def create_notification_and_mention_for(user, sender, msg)
+    Notification
+      .create!(
+        notification_type: Notification.types[:chat_mention],
+        user: user,
+        high_priority: true,
+        read: false,
+        data: {
+          message: "chat.mention_notification",
+          chat_message_id: msg.id,
+          chat_channel_id: msg.chat_channel_id,
+          chat_channel_title: msg.chat_channel.title(user),
+          chat_channel_slug: msg.chat_channel.slug,
+          mentioned_by_username: sender.username,
+        }.to_json,
+      )
+      .tap do |notification|
+        Chat::Mention.create!(user: user, chat_message: msg, notification: notification)
+      end
+  end
+end
diff --git a/plugins/chat/spec/services/chat/update_user_thread_last_read_spec.rb b/plugins/chat/spec/services/chat/update_user_thread_last_read_spec.rb
new file mode 100644
index 00000000000..fcf8ae1863f
--- /dev/null
+++ b/plugins/chat/spec/services/chat/update_user_thread_last_read_spec.rb
@@ -0,0 +1,91 @@
+# frozen_string_literal: true
+
+RSpec.describe Chat::UpdateUserThreadLastRead do
+  describe Chat::UpdateUserThreadLastRead::Contract, type: :model do
+    it { is_expected.to validate_presence_of :channel_id }
+    it { is_expected.to validate_presence_of :thread_id }
+  end
+
+  describe ".call" do
+    subject(:result) { described_class.call(params) }
+
+    fab!(:current_user) { Fabricate(:user) }
+    fab!(:channel) { Fabricate(:chat_channel) }
+    fab!(:thread) { Fabricate(:chat_thread, channel: channel) }
+
+    let(:guardian) { Guardian.new(current_user) }
+    let(:params) { { guardian: guardian, channel_id: channel.id, thread_id: thread.id } }
+
+    context "when params are not valid" do
+      before { params.delete(:thread_id) }
+
+      it { is_expected.to fail_a_contract }
+    end
+
+    context "when params are valid" do
+      context "when user can’t access the channel" do
+        fab!(:channel) { Fabricate(:private_category_channel) }
+        fab!(:thread) { Fabricate(:chat_thread, channel: channel) }
+
+        it { is_expected.to fail_a_policy(:invalid_access) }
+      end
+
+      context "when thread cannot be found" do
+        before { params[:channel_id] = Fabricate(:chat_channel).id }
+
+        it { is_expected.to fail_to_find_a_model(:thread) }
+      end
+
+      context "when everything is fine" do
+        fab!(:notification_1) do
+          Fabricate(
+            :notification,
+            notification_type: Notification.types[:chat_mention],
+            user: current_user,
+          )
+        end
+        fab!(:notification_2) do
+          Fabricate(
+            :notification,
+            notification_type: Notification.types[:chat_mention],
+            user: current_user,
+          )
+        end
+
+        let(:messages) { MessageBus.track_publish { result } }
+
+        before do
+          Jobs.run_immediately!
+          Chat::Mention.create!(
+            notification: notification_1,
+            user: current_user,
+            chat_message: Fabricate(:chat_message, chat_channel: channel, thread: thread),
+          )
+          Chat::Mention.create!(
+            notification: notification_2,
+            user: current_user,
+            chat_message: Fabricate(:chat_message, chat_channel: channel, thread: thread),
+          )
+        end
+
+        it "sets the service result as successful" do
+          expect(result).to be_a_success
+        end
+
+        it "marks existing notifications related to all messages in the thread as read" do
+          expect { result }.to change {
+            Notification.where(
+              notification_type: Notification.types[:chat_mention],
+              user: current_user,
+              read: false,
+            ).count
+          }.by(-2)
+        end
+
+        it "publishes new last read to clients" do
+          expect(messages.map(&:channel)).to include("/chat/user-tracking-state/#{current_user.id}")
+        end
+      end
+    end
+  end
+end
diff --git a/plugins/chat/spec/system/user_menu_notifications/sidebar_spec.rb b/plugins/chat/spec/system/user_menu_notifications/sidebar_spec.rb
index a9fe1464dea..3bfa6ad19ac 100644
--- a/plugins/chat/spec/system/user_menu_notifications/sidebar_spec.rb
+++ b/plugins/chat/spec/system/user_menu_notifications/sidebar_spec.rb
@@ -129,6 +129,31 @@ RSpec.describe "User menu notifications | sidebar", type: :system, js: true do
             href: "/chat/c/#{channel_1.slug}/#{channel_1.id}/#{message.id}",
           )
         end
+
+        it "shows a mention notification when the message is in a thread" do
+          Jobs.run_immediately!
+
+          message =
+            Chat::MessageCreator.create(
+              chat_channel: channel_1,
+              user: other_user,
+              content: "this is fine @#{current_user.username}",
+              thread_id: Fabricate(:chat_thread, channel: channel_1).id,
+            ).chat_message
+
+          visit("/")
+
+          find(".header-dropdown-toggle.current-user").click
+          within("#user-menu-button-chat-notifications") do |panel|
+            expect(panel).to have_content(1)
+            panel.click
+          end
+
+          expect(find("#quick-access-chat-notifications")).to have_link(
+            I18n.t("js.notifications.popup.chat_mention.direct", channel: channel_1.name),
+            href: "/chat/c/#{channel_1.slug}/#{channel_1.id}/t/#{message.thread_id}",
+          )
+        end
       end
 
       context "when @all" do