diff --git a/app/assets/javascripts/discourse/models/topic-list.js.es6 b/app/assets/javascripts/discourse/models/topic-list.js.es6
index 6c90b31ab3c..5346fd977ea 100644
--- a/app/assets/javascripts/discourse/models/topic-list.js.es6
+++ b/app/assets/javascripts/discourse/models/topic-list.js.es6
@@ -98,13 +98,22 @@ TopicList.reopenClass({
     if (!result) { return; }
 
     // Stitch together our side loaded data
+
     const categories = Discourse.Category.list(),
-          users = Model.extractByKey(result.users, Discourse.User);
+          users = Model.extractByKey(result.users, Discourse.User),
+          groups = Model.extractByKey(result.primary_groups, Ember.Object);
 
     return result.topic_list.topics.map(function (t) {
       t.category = categories.findBy('id', t.category_id);
       t.posters.forEach(function(p) {
         p.user = users[p.user_id];
+        p.extraClasses = p.extras;
+        if (p.primary_group_id) {
+          p.primary_group = groups[p.primary_group_id];
+          if (p.primary_group) {
+            p.extraClasses += ` group-${p.primary_group.name}`;
+          }
+        }
       });
       if (t.participants) {
         t.participants.forEach(function(p) {
diff --git a/app/assets/javascripts/discourse/templates/list/posters-column.raw.hbs b/app/assets/javascripts/discourse/templates/list/posters-column.raw.hbs
index 71317223b4b..8a76f021914 100644
--- a/app/assets/javascripts/discourse/templates/list/posters-column.raw.hbs
+++ b/app/assets/javascripts/discourse/templates/list/posters-column.raw.hbs
@@ -1,5 +1,5 @@
 <td class='posters'>
 {{#each posters as |poster|}}
-<a href="{{poster.user.path}}" data-user-card="{{poster.user.username}}" class="{{poster.extras}}">{{avatar poster avatarTemplatePath="user.avatar_template" usernamePath="user.username" imageSize="small"}}</a>
+<a href="{{poster.user.path}}" data-user-card="{{poster.user.username}}" class="{{poster.extraClasses}}">{{avatar poster avatarTemplatePath="user.avatar_template" usernamePath="user.username" imageSize="small"}}</a>
 {{/each}}
 </td>
diff --git a/app/models/topic.rb b/app/models/topic.rb
index 90517540f78..be414d6b59d 100644
--- a/app/models/topic.rb
+++ b/app/models/topic.rb
@@ -816,7 +816,7 @@ SQL
     update_column(:like_count, Post.where(topic_id: id).sum(:like_count))
   end
 
-  def posters_summary(options = {})
+  def posters_summary(options = {}) # avatar lookup in options
     @posters_summary ||= TopicPostersSummary.new(self, options).summary
   end
 
diff --git a/app/models/topic_list.rb b/app/models/topic_list.rb
index b26db3cff2c..16dc5ea6e27 100644
--- a/app/models/topic_list.rb
+++ b/app/models/topic_list.rb
@@ -1,4 +1,5 @@
 require_dependency 'avatar_lookup'
+require_dependency 'primary_group_lookup'
 
 class TopicList
   include ActiveModel::Serialization
@@ -108,7 +109,11 @@ class TopicList
         ft.user_data.post_action_data = {post_action_type => actions}
       end
 
-      ft.posters = ft.posters_summary(avatar_lookup: avatar_lookup)
+      ft.posters = ft.posters_summary(
+        avatar_lookup: avatar_lookup,
+        primary_group_lookup: PrimaryGroupLookup.new(user_ids)
+      )
+
       ft.participants = ft.participants_summary(avatar_lookup: avatar_lookup, user: @current_user)
       ft.topic_list = self
     end
diff --git a/app/models/topic_participants_summary.rb b/app/models/topic_participants_summary.rb
index f72a5fb6cdd..424e203c482 100644
--- a/app/models/topic_participants_summary.rb
+++ b/app/models/topic_participants_summary.rb
@@ -1,3 +1,4 @@
+# This is used on a topic page
 class TopicParticipantsSummary
   attr_reader :topic, :options
 
diff --git a/app/models/topic_poster.rb b/app/models/topic_poster.rb
index 7e32aa83db4..ec3a88e2a26 100644
--- a/app/models/topic_poster.rb
+++ b/app/models/topic_poster.rb
@@ -1,14 +1,15 @@
 class TopicPoster < OpenStruct
   include ActiveModel::Serialization
 
-  attr_accessor :user, :description, :extras, :id
+  attr_accessor :user, :description, :extras, :id, :primary_group
 
   def attributes
     {
       'user' => user,
       'description' => description,
       'extras' => extras,
-      'id' => id
+      'id' => id,
+      'primary_group' => primary_group
     }
   end
 
diff --git a/app/models/topic_posters_summary.rb b/app/models/topic_posters_summary.rb
index c000505ead2..7723bf338cd 100644
--- a/app/models/topic_posters_summary.rb
+++ b/app/models/topic_posters_summary.rb
@@ -1,3 +1,4 @@
+# This is used in topic lists
 class TopicPostersSummary
   attr_reader :topic, :options
 
@@ -16,6 +17,7 @@ class TopicPostersSummary
     TopicPoster.new.tap do |topic_poster|
       topic_poster.user = user
       topic_poster.description = descriptions_for(user)
+      topic_poster.primary_group = primary_group_lookup[user.id]
       if topic.last_post_user_id == user.id
         topic_poster.extras = 'latest'
         topic_poster.extras << ' single' if user_ids.uniq.size == 1
@@ -74,4 +76,8 @@ class TopicPostersSummary
   def avatar_lookup
     @avatar_lookup ||= options[:avatar_lookup] || AvatarLookup.new(user_ids)
   end
+
+  def primary_group_lookup
+    @primary_group_lookup ||= options[:primary_group_lookup] || PrimaryGroupLookup.new(user_ids)
+  end
 end
diff --git a/app/serializers/primary_group_serializer.rb b/app/serializers/primary_group_serializer.rb
new file mode 100644
index 00000000000..c9f7130e4e0
--- /dev/null
+++ b/app/serializers/primary_group_serializer.rb
@@ -0,0 +1,3 @@
+class PrimaryGroupSerializer < ApplicationSerializer
+  attributes :id, :name, :flair_url, :flair_bg_color, :flair_color
+end
diff --git a/app/serializers/topic_poster_serializer.rb b/app/serializers/topic_poster_serializer.rb
index a3c3f2864e3..9d182b9121d 100644
--- a/app/serializers/topic_poster_serializer.rb
+++ b/app/serializers/topic_poster_serializer.rb
@@ -1,4 +1,5 @@
 class TopicPosterSerializer < ApplicationSerializer
   attributes :extras, :description
   has_one :user, serializer: BasicUserSerializer
+  has_one :primary_group, serializer: PrimaryGroupSerializer
 end
diff --git a/lib/primary_group_lookup.rb b/lib/primary_group_lookup.rb
new file mode 100644
index 00000000000..c61bb1b7e5e
--- /dev/null
+++ b/lib/primary_group_lookup.rb
@@ -0,0 +1,37 @@
+class PrimaryGroupLookup
+  def initialize(user_ids=[])
+    @user_ids = user_ids.tap(&:compact!).tap(&:uniq!).tap(&:flatten!)
+  end
+
+  # Lookup primary group for a given user id
+  def [](user_id)
+    users[user_id]
+  end
+
+  private
+
+  def self.lookup_columns
+    @lookup_columns ||= %i{id name flair_url flair_bg_color flair_color}
+  end
+
+  def users
+    @users ||= user_lookup_hash
+  end
+
+  def user_lookup_hash
+    users_with_primary_group = User.where(id: @user_ids)
+        .where.not(primary_group_id: nil)
+        .select(:id, :primary_group_id)
+
+    group_lookup = {}
+    group_ids = users_with_primary_group.map(&:primary_group_id).compact
+    Group.where(id: group_ids).select(self.class.lookup_columns)
+         .each { |g| group_lookup[g.id] = g }
+
+    hash = {}
+    users_with_primary_group.each do |u|
+      hash[u.id] = group_lookup[u.primary_group_id]
+    end
+    hash
+  end
+end