diff --git a/runtime/doc/autocmd.txt b/runtime/doc/autocmd.txt
index bb84966228..ca816851dd 100644
--- a/runtime/doc/autocmd.txt
+++ b/runtime/doc/autocmd.txt
@@ -466,6 +466,16 @@ CompleteDone			After Insert mode completion is done.  Either
 				CompleteDonePre if you need it.
 				|v:completed_item| gives the completed item.
 
+				Sets these |v:event| keys:
+				    reason	Reason for completion being
+						done. Can be one of:
+						- "accept": completion was
+						  accepted using |complete_CTRL-Y|.
+						- "cancel": completion was cancelled
+						  using |complete_CTRL-E|, pressing
+						  a non-keyword character, or
+						  triggering a new completion.
+
 							*CursorHold*
 CursorHold			When the user doesn't press a key for the time
 				specified with 'updatetime'.  Not triggered
diff --git a/runtime/doc/news.txt b/runtime/doc/news.txt
index f8bc983441..03f6f7f8fd 100644
--- a/runtime/doc/news.txt
+++ b/runtime/doc/news.txt
@@ -130,6 +130,9 @@ UI
 • TODO
 
 
+• |CompleteDone| now sets the `reason` key in `v:event` which specifies the reason
+  for completion being done.
+
 ==============================================================================
 CHANGED FEATURES                                                 *news-changed*
 
diff --git a/runtime/doc/vvars.txt b/runtime/doc/vvars.txt
index de7f23a34d..15d836a83d 100644
--- a/runtime/doc/vvars.txt
+++ b/runtime/doc/vvars.txt
@@ -187,6 +187,7 @@ v:event
 		  changed_window   Is |v:true| if the event fired while
 		                   changing window  (or tab) on |DirChanged|.
 		  status           Job status or exit code, -1 means "unknown". |TermClose|
+		  reason           Reason for completion being done. |CompleteDone|
 
 				*v:exception* *exception-variable*
 v:exception
diff --git a/runtime/lua/vim/_meta/vvars.lua b/runtime/lua/vim/_meta/vvars.lua
index 1660d1dd6c..e00402ab3f 100644
--- a/runtime/lua/vim/_meta/vvars.lua
+++ b/runtime/lua/vim/_meta/vvars.lua
@@ -195,6 +195,7 @@ vim.v.errors = ...
 ---   changed_window   Is `v:true` if the event fired while
 ---                    changing window  (or tab) on `DirChanged`.
 ---   status           Job status or exit code, -1 means "unknown". `TermClose`
+---   reason           Reason for completion being done. `CompleteDone`
 --- @type any
 vim.v.event = ...
 
diff --git a/src/nvim/insexpand.c b/src/nvim/insexpand.c
index cec1e4a9e3..b557b9802e 100644
--- a/src/nvim/insexpand.c
+++ b/src/nvim/insexpand.c
@@ -568,6 +568,18 @@ static bool is_first_match(const compl_T *const match)
   return match == compl_first_match;
 }
 
+static void do_autocmd_completedone(int c)
+{
+  save_v_event_T save_v_event;
+  dict_T *v_event = get_v_event(&save_v_event);
+
+  tv_dict_add_str(v_event, S_LEN("reason"), (c == Ctrl_Y ? "accept" : "cancel"));
+  tv_dict_set_keys_readonly(v_event);
+
+  ins_apply_autocmds(EVENT_COMPLETEDONE);
+  restore_v_event(v_event, &save_v_event);
+}
+
 /// Check that character "c" is part of the item currently being
 /// completed.  Used to decide whether to abandon complete mode when the menu
 /// is visible.
@@ -2110,7 +2122,7 @@ static bool ins_compl_stop(const int c, const int prev_mode, bool retval)
   }
   // Trigger the CompleteDone event to give scripts a chance to act
   // upon the end of completion.
-  ins_apply_autocmds(EVENT_COMPLETEDONE);
+  do_autocmd_completedone(c);
 
   return retval;
 }
@@ -2199,7 +2211,7 @@ bool ins_compl_prep(int c)
   } else if (ctrl_x_mode == CTRL_X_LOCAL_MSG) {
     // Trigger the CompleteDone event to give scripts a chance to act
     // upon the (possibly failed) completion.
-    ins_apply_autocmds(EVENT_COMPLETEDONE);
+    do_autocmd_completedone(c);
   }
 
   may_trigger_modechanged();
diff --git a/src/nvim/vvars.lua b/src/nvim/vvars.lua
index 224edfaf6e..2f43f8b32b 100644
--- a/src/nvim/vvars.lua
+++ b/src/nvim/vvars.lua
@@ -215,6 +215,7 @@ M.vars = {
         changed_window   Is |v:true| if the event fired while
                          changing window  (or tab) on |DirChanged|.
         status           Job status or exit code, -1 means "unknown". |TermClose|
+        reason           Reason for completion being done. |CompleteDone|
     ]=],
   },
   exception = {
diff --git a/test/functional/autocmd/completedone_spec.lua b/test/functional/autocmd/completedone_spec.lua
new file mode 100644
index 0000000000..33beb16db2
--- /dev/null
+++ b/test/functional/autocmd/completedone_spec.lua
@@ -0,0 +1,41 @@
+local t = require('test.testutil')
+local n = require('test.functional.testnvim')()
+
+local clear = n.clear
+local command = n.command
+local call = n.call
+local feed = n.feed
+local eval = n.eval
+local eq = t.eq
+
+describe('CompleteDone', function()
+  before_each(clear)
+
+  describe('sets v:event.reason', function()
+    before_each(function()
+      clear()
+      command('autocmd CompleteDone * let g:donereason = v:event.reason')
+      feed('i')
+      call('complete', call('col', '.'), { 'foo', 'bar' })
+    end)
+
+    it('accept', function()
+      feed('<C-y>')
+      eq('accept', eval('g:donereason'))
+    end)
+    describe('cancel', function()
+      it('on <C-e>', function()
+        feed('<C-e>')
+        eq('cancel', eval('g:donereason'))
+      end)
+      it('on non-keyword character', function()
+        feed('<Esc>')
+        eq('cancel', eval('g:donereason'))
+      end)
+      it('when overriden by another complete()', function()
+        call('complete', call('col', '.'), { 'bar', 'baz' })
+        eq('cancel', eval('g:donereason'))
+      end)
+    end)
+  end)
+end)