The 50-year-old Cougar Town star and McDaid shared the news Friday in two tweets.
"I'm engaged to him!" the Friends alum wrote on Twitter along with a photo of the couple.
"I'm engaged to her!" McDaid tweeted with the same photo.
The couple's engagement comes two months after McDaid's pal, British singer Ed Sheeran, revealed the two were living together.
Cox and McDaid have been dating since 2013. The marriage will be the first for the musician and the second for the actress, who tied the knot to actor David Arquette in 1999.