diff --git a/app/assets/javascripts/commons/polyfills.js b/app/assets/javascripts/commons/polyfills.js
index d0cc4897aeb..a4394ab7e92 100644
--- a/app/assets/javascripts/commons/polyfills.js
+++ b/app/assets/javascripts/commons/polyfills.js
@@ -12,6 +12,7 @@ import 'core-js/es/promise/finally';
 import 'core-js/es/string/code-point-at';
 import 'core-js/es/string/from-code-point';
 import 'core-js/es/string/includes';
+import 'core-js/es/string/starts-with';
 import 'core-js/es/symbol';
 import 'core-js/es/map';
 import 'core-js/es/weak-map';
diff --git a/app/assets/javascripts/gfm_auto_complete.js b/app/assets/javascripts/gfm_auto_complete.js
index 3b73dd83c9f..b308cd9c236 100644
--- a/app/assets/javascripts/gfm_auto_complete.js
+++ b/app/assets/javascripts/gfm_auto_complete.js
@@ -318,6 +318,7 @@ class GfmAutoComplete {
   }
 
   setupLabels($input) {
+    const instance = this;
     const fetchData = this.fetchData.bind(this);
     const LABEL_COMMAND = { LABEL: '/label', UNLABEL: '/unlabel', RELABEL: '/relabel' };
     let command = '';
@@ -348,7 +349,6 @@ class GfmAutoComplete {
           }));
         },
         matcher(flag, subtext) {
-          const match = GfmAutoComplete.defaultMatcher(flag, subtext, this.app.controllers);
           const subtextNodes = subtext
             .split(/\n+/g)
             .pop()
@@ -366,6 +366,27 @@ class GfmAutoComplete {
             return null;
           });
 
+          // If any label matches the inserted text after the last `~`, suggest those labels,
+          // even if any spaces or funky characters were typed.
+          // This allows matching labels like "Accepting merge requests".
+          const labels = instance.cachedData[flag];
+          if (labels) {
+            if (!subtext.includes(flag)) {
+              // Do not match if there is no `~` before the cursor
+              return null;
+            }
+            const lastCandidate = subtext.split(flag).pop();
+            if (labels.find(label => label.title.startsWith(lastCandidate))) {
+              return lastCandidate;
+            }
+          } else {
+            // Load all labels into the autocompleter.
+            // This needs to happen if e.g. editing a label in an existing comment, because normally
+            // label data would only be loaded only once you type `~`.
+            fetchData(this.$inputor, this.at);
+          }
+
+          const match = GfmAutoComplete.defaultMatcher(flag, subtext, this.app.controllers);
           return match && match.length ? match[1] : null;
         },
         filter(query, data, searchKey) {
@@ -563,8 +584,9 @@ class GfmAutoComplete {
     const accentAChar = decodeURI('%C3%80');
     const accentYChar = decodeURI('%C3%BF');
 
+    // Holy regex, batman!
     const regexp = new RegExp(
-      `^(?:\\B|[^a-zA-Z0-9_\`${atSymbolsWithoutBar}]|\\s)${resultantFlag}(?!${atSymbolsWithBar})((?:[A-Za-z${accentAChar}-${accentYChar}0-9_'.+-]|[^\\x00-\\x7a])*)$`,
+      `^(?:\\B|[^a-zA-Z0-9_\`${atSymbolsWithoutBar}]|\\s)${resultantFlag}(?!${atSymbolsWithBar})((?:[A-Za-z${accentAChar}-${accentYChar}0-9_'.+-:]|[^\\x00-\\x7a])*)$`,
       'gi',
     );
 
diff --git a/changelogs/unreleased/mh-colon-autocomplete.yml b/changelogs/unreleased/mh-colon-autocomplete.yml
new file mode 100644
index 00000000000..8b169c22588
--- /dev/null
+++ b/changelogs/unreleased/mh-colon-autocomplete.yml
@@ -0,0 +1,5 @@
+---
+title: Allow auto-completing scoped labels
+merge_request: 29749
+author:
+type: added
diff --git a/spec/features/issues/gfm_autocomplete_spec.rb b/spec/features/issues/gfm_autocomplete_spec.rb
index 8eb413bdd8d..40845ec48f9 100644
--- a/spec/features/issues/gfm_autocomplete_spec.rb
+++ b/spec/features/issues/gfm_autocomplete_spec.rb
@@ -3,14 +3,14 @@ require 'rails_helper'
 describe 'GFM autocomplete', :js do
   let(:issue_xss_title) { 'This will execute alert<img src=x onerror=alert(2)&lt;img src=x onerror=alert(1)&gt;' }
   let(:user_xss_title) { 'eve <img src=x onerror=alert(2)&lt;img src=x onerror=alert(1)&gt;' }
-  let(:label_xss_title) { 'alert label &lt;img src=x onerror="alert(\'Hello xss\');" a'}
+  let(:label_xss_title) { 'alert label &lt;img src=x onerror="alert(\'Hello xss\');" a' }
   let(:milestone_xss_title) { 'alert milestone &lt;img src=x onerror="alert(\'Hello xss\');" a' }
 
   let(:user_xss) { create(:user, name: user_xss_title, username: 'xss.user') }
-  let(:user)    { create(:user, name: '💃speciąl someone💃', username: 'someone.special') }
+  let(:user) { create(:user, name: '💃speciąl someone💃', username: 'someone.special') }
   let(:project) { create(:project) }
   let(:label) { create(:label, project: project, title: 'special+') }
-  let(:issue)   { create(:issue, project: project) }
+  let(:issue) { create(:issue, project: project) }
 
   before do
     project.add_maintainer(user)
@@ -293,6 +293,70 @@ describe 'GFM autocomplete', :js do
         expect(find('.atwho-view-ul').text).to have_content('alert label')
       end
     end
+
+    it 'allows colons when autocompleting scoped labels' do
+      create(:label, project: project, title: 'scoped:label')
+
+      note = find('#note-body')
+      type(note, '~scoped:')
+
+      wait_for_requests
+
+      page.within '.atwho-container #at-view-labels' do
+        expect(find('.atwho-view-ul').text).to have_content('scoped:label')
+      end
+    end
+
+    it 'allows colons when autocompleting scoped labels with double colons' do
+      create(:label, project: project, title: 'scoped::label')
+
+      note = find('#note-body')
+      type(note, '~scoped::')
+
+      wait_for_requests
+
+      page.within '.atwho-container #at-view-labels' do
+        expect(find('.atwho-view-ul').text).to have_content('scoped::label')
+      end
+    end
+
+    it 'allows spaces when autocompleting multi-word labels' do
+      create(:label, project: project, title: 'Accepting merge requests')
+
+      note = find('#note-body')
+      type(note, '~Accepting merge')
+
+      wait_for_requests
+
+      page.within '.atwho-container #at-view-labels' do
+        expect(find('.atwho-view-ul').text).to have_content('Accepting merge requests')
+      end
+    end
+
+    it 'only autocompletes the latest label' do
+      create(:label, project: project, title: 'Accepting merge requests')
+      create(:label, project: project, title: 'Accepting job applicants')
+
+      note = find('#note-body')
+      type(note, '~Accepting merge requests foo bar ~Accepting job')
+
+      wait_for_requests
+
+      page.within '.atwho-container #at-view-labels' do
+        expect(find('.atwho-view-ul').text).to have_content('Accepting job applicants')
+      end
+    end
+
+    it 'does not autocomplete labels if no tilde is typed' do
+      create(:label, project: project, title: 'Accepting merge requests')
+
+      note = find('#note-body')
+      type(note, 'Accepting merge')
+
+      wait_for_requests
+
+      expect(page).not_to have_css('.atwho-container #at-view-labels')
+    end
   end
 
   shared_examples 'autocomplete suggestions' do