diff --git a/app/assets/javascripts/pages/projects/project.js b/app/assets/javascripts/pages/projects/project.js
index fdcbcc236c1..34a13eb3251 100644
--- a/app/assets/javascripts/pages/projects/project.js
+++ b/app/assets/javascripts/pages/projects/project.js
@@ -61,6 +61,13 @@ export default class Project {
         .remove();
       return e.preventDefault();
     });
+    $('.hide-auto-devops-implicitly-enabled-banner').on('click', function(e) {
+      const projectId = $(this).data('project-id');
+      const cookieKey = `hide_auto_devops_implicitly_enabled_banner_${projectId}`;
+      Cookies.set(cookieKey, 'false');
+      $(this).parents('.auto-devops-implicitly-enabled-banner').remove();
+      return e.preventDefault();
+    });
     Project.projectSelectDropdown();
   }
 
diff --git a/app/helpers/projects_helper.rb b/app/helpers/projects_helper.rb
index 80b45176a62..7a9b63d8852 100644
--- a/app/helpers/projects_helper.rb
+++ b/app/helpers/projects_helper.rb
@@ -203,6 +203,14 @@ module ProjectsHelper
       current_user.require_extra_setup_for_git_auth?
   end
 
+  def show_auto_devops_implicitly_enabled_banner?(project)
+    cookie_key = "hide_auto_devops_implicitly_enabled_banner_#{project.id}"
+
+    project.has_auto_devops_implicitly_enabled? &&
+      cookies[cookie_key.to_sym].blank? &&
+      (project.owner == current_user || project.team.maintainer?(current_user))
+  end
+
   def link_to_set_password
     if current_user.require_password_creation_for_git?
       link_to s_('SetPasswordToCloneLink|set a password'), edit_profile_password_path
diff --git a/app/views/projects/_flash_messages.html.haml b/app/views/projects/_flash_messages.html.haml
index 0175b519867..7a5fff96676 100644
--- a/app/views/projects/_flash_messages.html.haml
+++ b/app/views/projects/_flash_messages.html.haml
@@ -5,3 +5,4 @@
   - if current_user && can?(current_user, :download_code, project)
     = render 'shared/no_ssh'
     = render 'shared/no_password'
+    = render 'shared/auto_devops_implicitly_enabled_banner', project: project
diff --git a/app/views/shared/_auto_devops_implicitly_enabled_banner.html.haml b/app/views/shared/_auto_devops_implicitly_enabled_banner.html.haml
new file mode 100644
index 00000000000..6c4607b2f16
--- /dev/null
+++ b/app/views/shared/_auto_devops_implicitly_enabled_banner.html.haml
@@ -0,0 +1,9 @@
+- if show_auto_devops_implicitly_enabled_banner?(project)
+  .auto-devops-implicitly-enabled-banner.alert.alert-warning
+    - more_information_link = link_to _('More information'), 'https://docs.gitlab.com/ee/topics/autodevops/', class: 'alert-link'
+    - auto_devops_message = s_("AutoDevOps|The Auto DevOps pipeline has been enabled and will be used if no alternative CI configuration file is found. %{more_information_link}") % { more_information_link: more_information_link }
+    = auto_devops_message.html_safe
+    .alert-link-group
+      = link_to _('Settings'), project_settings_ci_cd_path(project), class: 'alert-link'
+      |
+      = link_to _('Dismiss'), '#', class: 'hide-auto-devops-implicitly-enabled-banner alert-link', data: { project_id: project.id }
diff --git a/changelogs/unreleased/50535-display-banner-to-notify-user-if-project-is-implicitly-opted-ado.yml b/changelogs/unreleased/50535-display-banner-to-notify-user-if-project-is-implicitly-opted-ado.yml
new file mode 100644
index 00000000000..23d4d504f04
--- /dev/null
+++ b/changelogs/unreleased/50535-display-banner-to-notify-user-if-project-is-implicitly-opted-ado.yml
@@ -0,0 +1,5 @@
+---
+title: Display banner on project page if AutoDevOps is implicitly enabled
+merge_request: 21503
+author:
+type: added
diff --git a/locale/gitlab.pot b/locale/gitlab.pot
index 9b78b9ad76f..9ce84cd53c7 100644
--- a/locale/gitlab.pot
+++ b/locale/gitlab.pot
@@ -739,6 +739,9 @@ msgstr ""
 msgid "AutoDevOps|Learn more in the %{link_to_documentation}"
 msgstr ""
 
+msgid "AutoDevOps|The Auto DevOps pipeline has been enabled and will be used if no alternative CI configuration file is found. %{more_information_link}"
+msgstr ""
+
 msgid "AutoDevOps|You can automatically build and test your application if you %{link_to_auto_devops_settings} for this project. You can automatically deploy it as well, if you %{link_to_add_kubernetes_cluster}."
 msgstr ""
 
diff --git a/spec/features/projects/show/user_interacts_with_auto_devops_banner_spec.rb b/spec/features/projects/show/user_interacts_with_auto_devops_banner_spec.rb
new file mode 100644
index 00000000000..baf715000a3
--- /dev/null
+++ b/spec/features/projects/show/user_interacts_with_auto_devops_banner_spec.rb
@@ -0,0 +1,61 @@
+# frozen_string_literal: true
+
+require 'spec_helper'
+
+describe 'Project > Show > User interacts with auto devops implicitly enabled banner' do
+  let(:project) { create(:project, :repository) }
+  let(:user) { create(:user) }
+
+  before do
+    project.add_user(user, role)
+    sign_in(user)
+  end
+
+  context 'when user does not have maintainer access' do
+    let(:role) { :developer }
+
+    context 'when AutoDevOps is implicitly enabled' do
+      it 'does not display AutoDevOps implicitly enabled banner' do
+        expect(page).not_to have_css('.auto-devops-implicitly-enabled-banner')
+      end
+    end
+  end
+
+  context 'when user has mantainer access' do
+    let(:role) { :maintainer }
+
+    context 'when AutoDevOps is implicitly enabled' do
+      before do
+        stub_application_setting(auto_devops_enabled: true)
+
+        visit project_path(project)
+      end
+
+      it 'display AutoDevOps implicitly enabled banner' do
+        expect(page).to have_css('.auto-devops-implicitly-enabled-banner')
+      end
+
+      context 'when user dismisses the banner', :js do
+        it 'does not display AutoDevOps implicitly enabled banner' do
+          find('.hide-auto-devops-implicitly-enabled-banner').click
+          wait_for_requests
+          visit project_path(project)
+
+          expect(page).not_to have_css('.auto-devops-implicitly-enabled-banner')
+        end
+      end
+    end
+
+    context 'when AutoDevOps is not implicitly enabled' do
+      before do
+        stub_application_setting(auto_devops_enabled: false)
+
+        visit project_path(project)
+      end
+
+      it 'does not display AutoDevOps implicitly enabled banner' do
+        expect(page).not_to have_css('.auto-devops-implicitly-enabled-banner')
+      end
+    end
+  end
+end