diff --git a/app/controllers/groups/milestones_controller.rb b/app/controllers/groups/milestones_controller.rb
index 7a7bcb1a3d2..f013d21275e 100644
--- a/app/controllers/groups/milestones_controller.rb
+++ b/app/controllers/groups/milestones_controller.rb
@@ -80,7 +80,8 @@ class Groups::MilestonesController < Groups::ApplicationController
     milestones = MilestonesFinder.new(search_params).execute
     legacy_milestones = GroupMilestone.build_collection(group, group_projects, params)
 
-    milestones + legacy_milestones
+    @sort = params[:sort] || 'due_date_asc'
+    MilestoneArray.sort(milestones + legacy_milestones, @sort)
   end
 
   def milestone
diff --git a/app/views/groups/milestones/index.html.haml b/app/views/groups/milestones/index.html.haml
index cb4fc69d5b8..6c199c52583 100644
--- a/app/views/groups/milestones/index.html.haml
+++ b/app/views/groups/milestones/index.html.haml
@@ -4,6 +4,7 @@
   = render 'shared/milestones_filter', counts: @milestone_states
 
   .nav-controls
+    = render 'shared/group_milestones_sort_dropdown'
     - if can?(current_user, :admin_milestones, @group)
       = link_to "New milestone", new_group_milestone_path(@group), class: "btn btn-new"
 
diff --git a/app/views/shared/_group_milestones_sort_dropdown.html.haml b/app/views/shared/_group_milestones_sort_dropdown.html.haml
new file mode 100644
index 00000000000..9b2f2fdcc93
--- /dev/null
+++ b/app/views/shared/_group_milestones_sort_dropdown.html.haml
@@ -0,0 +1,22 @@
+.dropdown.inline.prepend-left-10
+  %button.dropdown-toggle{ type: 'button', data: { toggle: 'dropdown' } }
+    %span.light
+    - if @sort.present?
+      = milestone_sort_options_hash[@sort]
+    - else
+      = sort_title_due_date_soon
+    = icon('chevron-down')
+  %ul.dropdown-menu.dropdown-menu-align-right.dropdown-menu-sort
+    %li
+      = link_to page_filter_path(sort: sort_value_due_date_soon, label: true) do
+        = sort_title_due_date_soon
+      = link_to page_filter_path(sort: sort_value_due_date_later, label: true) do
+        = sort_title_due_date_later
+      = link_to page_filter_path(sort: sort_value_start_date_soon, label: true) do
+        = sort_title_start_date_soon
+      = link_to page_filter_path(sort: sort_value_start_date_later, label: true) do
+        = sort_title_start_date_later
+      = link_to page_filter_path(sort: sort_value_name, label: true) do
+        = sort_title_name_asc
+      = link_to page_filter_path(sort: sort_value_name_desc, label: true) do
+        = sort_title_name_desc
diff --git a/changelogs/unreleased/39720-group-milestone-sorting.yml b/changelogs/unreleased/39720-group-milestone-sorting.yml
new file mode 100644
index 00000000000..15ef87fa567
--- /dev/null
+++ b/changelogs/unreleased/39720-group-milestone-sorting.yml
@@ -0,0 +1,5 @@
+---
+title: Add dropdown sort to group milestones
+merge_request: 15230
+author: George Andrinopoulos
+type: added
diff --git a/lib/milestone_array.rb b/lib/milestone_array.rb
new file mode 100644
index 00000000000..9b3f2acc123
--- /dev/null
+++ b/lib/milestone_array.rb
@@ -0,0 +1,40 @@
+module MilestoneArray
+  class << self
+    def sort(array, sort_method)
+      case sort_method
+      when 'due_date_asc'
+        sort_asc_nulls_last(array, 'due_date')
+      when 'due_date_desc'
+        sort_desc_nulls_last(array, 'due_date')
+      when 'start_date_asc'
+        sort_asc_nulls_last(array, 'start_date')
+      when 'start_date_desc'
+        sort_desc_nulls_last(array, 'start_date')
+      when 'name_asc'
+        sort_asc(array, 'title')
+      when 'name_desc'
+        sort_desc(array, 'title')
+      else
+        array
+      end
+    end
+
+    private
+
+    def sort_asc_nulls_last(array, attribute)
+      array.select(&attribute.to_sym).sort_by(&attribute.to_sym) + array.reject(&attribute.to_sym)
+    end
+
+    def sort_desc_nulls_last(array, attribute)
+      array.select(&attribute.to_sym).sort_by(&attribute.to_sym).reverse + array.reject(&attribute.to_sym)
+    end
+
+    def sort_asc(array, attribute)
+      array.sort_by(&attribute.to_sym)
+    end
+
+    def sort_desc(array, attribute)
+      array.sort_by(&attribute.to_sym).reverse
+    end
+  end
+end
diff --git a/spec/features/groups/milestones_sorting_spec.rb b/spec/features/groups/milestones_sorting_spec.rb
new file mode 100644
index 00000000000..3bd59587535
--- /dev/null
+++ b/spec/features/groups/milestones_sorting_spec.rb
@@ -0,0 +1,46 @@
+require 'spec_helper'
+
+feature 'Milestones sorting', :js do
+  let(:group) { create(:group) }
+  let!(:project) { create(:project_empty_repo, group: group) }
+  let!(:other_project) { create(:project_empty_repo, group: group) }
+  let!(:project_milestone1) { create(:milestone, project: project, title: 'v1.0', due_date: 10.days.from_now) }
+  let!(:other_project_milestone1) { create(:milestone, project: other_project, title: 'v1.0', due_date: 10.days.from_now) }
+  let!(:project_milestone2) { create(:milestone, project: project, title: 'v2.0', due_date: 5.days.from_now) }
+  let!(:other_project_milestone2) { create(:milestone, project: other_project, title: 'v2.0', due_date: 5.days.from_now) }
+  let(:user) { create(:group_member, :master, user: create(:user), group: group ).user }
+
+  before do
+    sign_in(user)
+  end
+
+  scenario 'visit group milestones and sort by due_date_asc' do
+    visit group_milestones_path(group)
+
+    expect(page).to have_button('Due soon')
+
+    # assert default sorting
+    within '.milestones' do
+      expect(page.all('ul.content-list > li').first.text).to include('v2.0')
+      expect(page.all('ul.content-list > li').last.text).to include('v1.0')
+    end
+
+    click_button 'Due soon'
+
+    sort_options = find('ul.dropdown-menu-sort li').all('a').collect(&:text)
+
+    expect(sort_options[0]).to eq('Due soon')
+    expect(sort_options[1]).to eq('Due later')
+    expect(sort_options[2]).to eq('Start soon')
+    expect(sort_options[3]).to eq('Start later')
+
+    click_link 'Due later'
+
+    expect(page).to have_button('Due later')
+
+    within '.milestones' do
+      expect(page.all('ul.content-list > li').first.text).to include('v1.0')
+      expect(page.all('ul.content-list > li').last.text).to include('v2.0')
+    end
+  end
+end
diff --git a/spec/lib/milestone_array_spec.rb b/spec/lib/milestone_array_spec.rb
new file mode 100644
index 00000000000..df91677b925
--- /dev/null
+++ b/spec/lib/milestone_array_spec.rb
@@ -0,0 +1,34 @@
+require 'spec_helper'
+
+describe MilestoneArray do
+  let(:object1) { instance_double("BirdMilestone", due_date: Time.now, start_date: Time.now - 15.days, title: 'v2.0') }
+  let(:object2) { instance_double("CatMilestone", due_date: Time.now - 1.day, start_date: nil, title: 'v1.0') }
+  let(:object3) { instance_double("DogMilestone", due_date: nil, start_date: Time.now - 30.days, title: 'v3.0') }
+  let(:array) { [object1, object3, object2] }
+
+  describe '#sort' do
+    it 'reorders array with due date in ascending order with nulls last' do
+      expect(described_class.sort(array, 'due_date_asc')).to eq([object2, object1, object3])
+    end
+
+    it 'reorders array with due date in desc order with nulls last' do
+      expect(described_class.sort(array, 'due_date_desc')).to eq([object1, object2, object3])
+    end
+
+    it 'reorders array with start date in ascending order with nulls last' do
+      expect(described_class.sort(array, 'start_date_asc')).to eq([object3, object1, object2])
+    end
+
+    it 'reorders array with start date in descending order with nulls last' do
+      expect(described_class.sort(array, 'start_date_desc')).to eq([object1, object3, object2])
+    end
+
+    it 'reorders array with title in ascending order' do
+      expect(described_class.sort(array, 'name_asc')).to eq([object2, object1, object3])
+    end
+
+    it 'reorders array with title in descending order' do
+      expect(described_class.sort(array, 'name_desc')).to eq([object3, object1, object2])
+    end
+  end
+end