The 32-year-old shared the news on Instagram on Saturday, sharing a photo of himself and Devlin with the caption: “What a birthday, my future wife.”
The news of the couple’s engagement prompted hundreds of congratulatory messages from fellow fighting stars and fans.
“Congratulations! Many blessings,” Holly Holm commented, while Artem Lobov wrote: “Congratulations to you and Dee!!!”
McGregor and Devlin, who share two children together, son Conor Jack Jr, three and daughter Croia, one, first started dating in 2008.
According to the former UFC champion, Devlin’s support over the years was integral to his successful career.
“Every day, since I started out in this game, she’s supported me,” McGregor previously told VIP Magazine. “She’d drive me to the gym, and she’d listen to all my dreams.
“Dee is a lifesaver for me. I wouldn’t be doing this if it wasn’t for her, and that’s for sure. I’m doing all of this for her.”
While Devlin did not post about the engagement on Instagram, her last post, shared on 14 July, is dedicated to McGregor.
“Happy Birthday to my everything. Let’s celebrate you today babe. I love you,” Devlin wrote alongside two photos of the couple.