Per Ben Rothenberg of the New York Times, Murray's camp confirmed he will pair up with Williams at this year's event from the All England Club.
Murray announced in January he would retire after this year's Wimbledon because of ongoing issues with his hip that have limited his ability since 2016.
"I spoke to my team, and I told them, 'I cannot keep doing this,'" Murray told reporters about his decision. "I needed to have an end point because I was sort of playing with no idea when the pain was going to stop. I felt like making that decision."
After undergoing hip resurfacing surgery in January, Murray sounded like he was having a change of heart. The two-time Wimbledon champion declared he was pain-free in March but didn't want to rush his body if he were to make a serious comeback attempt.
"I would hate to go on the court at Wimbledon and for something bad to happen," he said. "Or to feel really bad and apprehensive and for it to go really badly. I wouldn't want that to happen."
Murray noted at the time playing doubles could be a "stepping stone" to test his body before trying to return to singles action. He's already scheduled to play in men's doubles with Pierre-Hugues Herbert.
Williams and Murray have been teasing a possible team-up leading into Wimbledon. Now that it is officially happening, two of tennis' biggest stars will have all eyes on them for the next two weeks.
Williams, who won her first-round singles match over Giulia Gatto-Monticone on Tuesday, previously won the mixed doubles title at Wimbledon in 1998 with Max Mirnyi.
Murray hasn't played mixed doubles at Wimbledon since 2006 with Kirsten Flipkens. They were eliminated in the second round as a wild-card entry.