diff --git a/CHANGELOG b/CHANGELOG
index 8510f374c3af33bcfcd8177c67b904b6d13a4bc3..851b7d5013a3d2e835ada8b6d19f3dea51d64791 100644
--- a/CHANGELOG
+++ b/CHANGELOG
@@ -34,6 +34,7 @@ v 8.13.0 (unreleased)
   - Notify the Merger about merge after successful build (Dimitris Karakasilis)
   - Fix broken repository 500 errors in project list
   - Close todos when accepting merge requests via the API !6486 (tonygambone)
+  - Changed Slack service user referencing from full name to username (Sebastian Poxhofer) 
 
 v 8.12.4 (unreleased)
 
diff --git a/app/models/project_services/slack_service/issue_message.rb b/app/models/project_services/slack_service/issue_message.rb
index 88e053ec19274d5ecbfcaf9fc13a78bbd145566a..cd87a79d0c607383f6c92b0c66cda190f095dcd4 100644
--- a/app/models/project_services/slack_service/issue_message.rb
+++ b/app/models/project_services/slack_service/issue_message.rb
@@ -11,7 +11,7 @@ class SlackService
     attr_reader :description
 
     def initialize(params)
-      @user_name = params[:user][:name]
+      @user_name = params[:user][:username]
       @project_name = params[:project_name]
       @project_url = params[:project_url]
 
diff --git a/app/models/project_services/slack_service/merge_message.rb b/app/models/project_services/slack_service/merge_message.rb
index 11fc691022bbfe23fc85ef05cd75c242f9891f67..b7615c960686177ef046d6b1ea25e46b6be15c8b 100644
--- a/app/models/project_services/slack_service/merge_message.rb
+++ b/app/models/project_services/slack_service/merge_message.rb
@@ -10,7 +10,7 @@ class SlackService
     attr_reader :title
 
     def initialize(params)
-      @user_name = params[:user][:name]
+      @user_name = params[:user][:username]
       @project_name = params[:project_name]
       @project_url = params[:project_url]
 
diff --git a/app/models/project_services/slack_service/note_message.rb b/app/models/project_services/slack_service/note_message.rb
index 89ba51cb6627ee3d3b48fb00363e0e99c3a60a31..9e84e90f38c8b633003c61d412345430c95d2afa 100644
--- a/app/models/project_services/slack_service/note_message.rb
+++ b/app/models/project_services/slack_service/note_message.rb
@@ -10,7 +10,7 @@ class SlackService
 
     def initialize(params)
       params = HashWithIndifferentAccess.new(params)
-      @user_name = params[:user][:name]
+      @user_name = params[:user][:username]
       @project_name = params[:project_name]
       @project_url = params[:project_url]
 
diff --git a/app/models/project_services/slack_service/wiki_page_message.rb b/app/models/project_services/slack_service/wiki_page_message.rb
index f336d9e7691d56fdc2109823c91c41c60590f895..160ca3ac11523fa32fe5c5a36f640e1050401c11 100644
--- a/app/models/project_services/slack_service/wiki_page_message.rb
+++ b/app/models/project_services/slack_service/wiki_page_message.rb
@@ -9,7 +9,7 @@ class SlackService
     attr_reader :description
 
     def initialize(params)
-      @user_name = params[:user][:name]
+      @user_name = params[:user][:username]
       @project_name = params[:project_name]
       @project_url = params[:project_url]
 
diff --git a/spec/models/project_services/slack_service/issue_message_spec.rb b/spec/models/project_services/slack_service/issue_message_spec.rb
index 0f8889bdf3c874ca933759ae1541226e185b84b5..98c36ec088dde79355b9a16943f194e68abbc285 100644
--- a/spec/models/project_services/slack_service/issue_message_spec.rb
+++ b/spec/models/project_services/slack_service/issue_message_spec.rb
@@ -7,7 +7,7 @@ describe SlackService::IssueMessage, models: true do
     {
       user: {
         name: 'Test User',
-        username: 'Test User'
+        username: 'test.user'
       },
       project_name: 'project_name',
       project_url: 'somewhere.com',
@@ -40,7 +40,7 @@ describe SlackService::IssueMessage, models: true do
   context 'open' do
     it 'returns a message regarding opening of issues' do
       expect(subject.pretext).to eq(
-        '<somewhere.com|[project_name>] Issue opened by Test User')
+        '<somewhere.com|[project_name>] Issue opened by test.user')
       expect(subject.attachments).to eq([
         {
           title: "#100 Issue title",
@@ -60,7 +60,7 @@ describe SlackService::IssueMessage, models: true do
 
     it 'returns a message regarding closing of issues' do
       expect(subject.pretext). to eq(
-        '<somewhere.com|[project_name>] Issue <url|#100 Issue title> closed by Test User')
+        '<somewhere.com|[project_name>] Issue <url|#100 Issue title> closed by test.user')
       expect(subject.attachments).to be_empty
     end
   end
diff --git a/spec/models/project_services/slack_service/merge_message_spec.rb b/spec/models/project_services/slack_service/merge_message_spec.rb
index 224c7ceabe881867792f93fe00f7b85085415386..c5c052d9af1b0e342bf0493f096f9ab7be7ad404 100644
--- a/spec/models/project_services/slack_service/merge_message_spec.rb
+++ b/spec/models/project_services/slack_service/merge_message_spec.rb
@@ -7,7 +7,7 @@ describe SlackService::MergeMessage, models: true do
     {
       user: {
           name: 'Test User',
-          username: 'Test User'
+          username: 'test.user'
       },
       project_name: 'project_name',
       project_url: 'somewhere.com',
@@ -31,7 +31,7 @@ describe SlackService::MergeMessage, models: true do
   context 'open' do
     it 'returns a message regarding opening of merge requests' do
       expect(subject.pretext).to eq(
-        'Test User opened <somewhere.com/merge_requests/100|merge request !100> '\
+        'test.user opened <somewhere.com/merge_requests/100|merge request !100> '\
         'in <somewhere.com|project_name>: *Issue title*')
       expect(subject.attachments).to be_empty
     end
@@ -43,7 +43,7 @@ describe SlackService::MergeMessage, models: true do
     end
     it 'returns a message regarding closing of merge requests' do
       expect(subject.pretext).to eq(
-        'Test User closed <somewhere.com/merge_requests/100|merge request !100> '\
+        'test.user closed <somewhere.com/merge_requests/100|merge request !100> '\
         'in <somewhere.com|project_name>: *Issue title*')
       expect(subject.attachments).to be_empty
     end
diff --git a/spec/models/project_services/slack_service/note_message_spec.rb b/spec/models/project_services/slack_service/note_message_spec.rb
index 41b93f08050833499baf90ca88a9ced8332f2399..38cfe4ad3e3c1ac7d803f7860573fe79dbd59729 100644
--- a/spec/models/project_services/slack_service/note_message_spec.rb
+++ b/spec/models/project_services/slack_service/note_message_spec.rb
@@ -7,7 +7,7 @@ describe SlackService::NoteMessage, models: true do
     @args = {
         user: {
             name: 'Test User',
-            username: 'username',
+            username: 'test.user',
             avatar_url: 'http://fakeavatar'
         },
         project_name: 'project_name',
@@ -37,7 +37,7 @@ describe SlackService::NoteMessage, models: true do
 
     it 'returns a message regarding notes on commits' do
       message = SlackService::NoteMessage.new(@args)
-      expect(message.pretext).to eq("Test User commented on " \
+      expect(message.pretext).to eq("test.user commented on " \
       "<url|commit 5f163b2b> in <somewhere.com|project_name>: " \
       "*Added a commit message*")
       expected_attachments = [
@@ -63,7 +63,7 @@ describe SlackService::NoteMessage, models: true do
 
     it 'returns a message regarding notes on a merge request' do
       message = SlackService::NoteMessage.new(@args)
-      expect(message.pretext).to eq("Test User commented on " \
+      expect(message.pretext).to eq("test.user commented on " \
       "<url|merge request !30> in <somewhere.com|project_name>: " \
       "*merge request title*")
       expected_attachments = [
@@ -90,7 +90,7 @@ describe SlackService::NoteMessage, models: true do
     it 'returns a message regarding notes on an issue' do
       message = SlackService::NoteMessage.new(@args)
       expect(message.pretext).to eq(
-        "Test User commented on " \
+        "test.user commented on " \
         "<url|issue #20> in <somewhere.com|project_name>: " \
         "*issue title*")
       expected_attachments = [
@@ -115,7 +115,7 @@ describe SlackService::NoteMessage, models: true do
 
     it 'returns a message regarding notes on a project snippet' do
       message = SlackService::NoteMessage.new(@args)
-      expect(message.pretext).to eq("Test User commented on " \
+      expect(message.pretext).to eq("test.user commented on " \
       "<url|snippet #5> in <somewhere.com|project_name>: " \
       "*snippet title*")
       expected_attachments = [
diff --git a/spec/models/project_services/slack_service/push_message_spec.rb b/spec/models/project_services/slack_service/push_message_spec.rb
index cda9ee670b0dcd13f0b2538129960a9915090e5e..17cd05e24f1291e4765fc70ae839f11e0da82c6f 100644
--- a/spec/models/project_services/slack_service/push_message_spec.rb
+++ b/spec/models/project_services/slack_service/push_message_spec.rb
@@ -9,7 +9,7 @@ describe SlackService::PushMessage, models: true do
       before: 'before',
       project_name: 'project_name',
       ref: 'refs/heads/master',
-      user_name: 'user_name',
+      user_name: 'test.user',
       project_url: 'url'
     }
   end
@@ -26,7 +26,7 @@ describe SlackService::PushMessage, models: true do
 
     it 'returns a message regarding pushes' do
       expect(subject.pretext).to eq(
-        'user_name pushed to branch <url/commits/master|master> of '\
+        'test.user pushed to branch <url/commits/master|master> of '\
         '<url|project_name> (<url/compare/before...after|Compare changes>)'
       )
       expect(subject.attachments).to eq([
@@ -46,13 +46,13 @@ describe SlackService::PushMessage, models: true do
         before: Gitlab::Git::BLANK_SHA,
         project_name: 'project_name',
         ref: 'refs/tags/new_tag',
-        user_name: 'user_name',
+        user_name: 'test.user',
         project_url: 'url'
       }
     end
 
     it 'returns a message regarding pushes' do
-      expect(subject.pretext).to eq('user_name pushed new tag ' \
+      expect(subject.pretext).to eq('test.user pushed new tag ' \
        '<url/commits/new_tag|new_tag> to ' \
        '<url|project_name>')
       expect(subject.attachments).to be_empty
@@ -66,7 +66,7 @@ describe SlackService::PushMessage, models: true do
 
     it 'returns a message regarding a new branch' do
       expect(subject.pretext).to eq(
-        'user_name pushed new branch <url/commits/master|master> to '\
+        'test.user pushed new branch <url/commits/master|master> to '\
         '<url|project_name>'
       )
       expect(subject.attachments).to be_empty
@@ -80,7 +80,7 @@ describe SlackService::PushMessage, models: true do
 
     it 'returns a message regarding a removed branch' do
       expect(subject.pretext).to eq(
-        'user_name removed branch master from <url|project_name>'
+        'test.user removed branch master from <url|project_name>'
       )
       expect(subject.attachments).to be_empty
     end
diff --git a/spec/models/project_services/slack_service/wiki_page_message_spec.rb b/spec/models/project_services/slack_service/wiki_page_message_spec.rb
index 13aea0b0600675a331eb883b889b298ce826f5d2..093911598b009e29a2a606c2231f0968e5cd82e1 100644
--- a/spec/models/project_services/slack_service/wiki_page_message_spec.rb
+++ b/spec/models/project_services/slack_service/wiki_page_message_spec.rb
@@ -7,7 +7,7 @@ describe SlackService::WikiPageMessage, models: true do
     {
       user: {
         name: 'Test User',
-        username: 'Test User'
+        username: 'test.user'
       },
       project_name: 'project_name',
       project_url: 'somewhere.com',
@@ -25,7 +25,7 @@ describe SlackService::WikiPageMessage, models: true do
 
       it 'returns a message that a new wiki page was created' do
         expect(subject.pretext).to eq(
-          'Test User created <url|wiki page> in <somewhere.com|project_name>: '\
+          'test.user created <url|wiki page> in <somewhere.com|project_name>: '\
           '*Wiki page title*')
       end
     end
@@ -35,7 +35,7 @@ describe SlackService::WikiPageMessage, models: true do
 
       it 'returns a message that a wiki page was updated' do
         expect(subject.pretext).to eq(
-          'Test User edited <url|wiki page> in <somewhere.com|project_name>: '\
+          'test.user edited <url|wiki page> in <somewhere.com|project_name>: '\
           '*Wiki page title*')
       end
     end