Congrats are in order for Conor McGregor and Dee Devlin -- the UFC superstar popped the question to his longtime GF ... and she said YES!!!

The couple -- who have been together for more than a decade -- made the news official on Saturday ... showing off a MASSIVE engagement ring.

The fighter posted about dropping to one knee before Devlin's 33rd birthday, which is August 9 ... but hints it may have happened around his birthday last month.

"What a birthday, my future wife !" Conor captioned his post on Instagram.

McGregor and Devlin have 2 children together -- 3-year-old Conor Jr. and almost 2-year-old Croia.

It's been an eventful 2020 for Conor ... he kicked it off by beating Cowboy Cerrone at UFC 246 ... and retired from MMA (for the third time) in June.

Conor and Dee have spent their time traveling all over the globe ever since ... including a lavish getaway in France.