The Murray-Williams partnership came just before the closing time of the mixed doubles draw on Wednesday and was confirmed by the 32-year-old Scottish player's representative.
The 23-Grand Slam winner Williams decided to join Murray, telling reporters after winning her first-round singles match at Wimbledon: "If you guys really want it, then maybe I will do it."
Murray and Williams are set to square off against Germany's Andreas Mies and Chile's Alexa Guarachi in the first round of the tournament.
Meanwhile, the former world No.1 Murray will pair up with Frenchman Pierre-Hugues Herbert in the men's doubles.
After Wimbledon, Murray may consider a singles return at the US Open, the last Grand Slam of the season, if he regains his form following a right hip surgery.
Murray first would have to compete at Cincinnati, a US Open tune-up event that he won twice in 2008 and 2011.
He was crowned the US Open champion in 2012 and afterward he defeated the current world No.1 Novak Djokovic of Serbia in the final match.
Last month, Murray won the men's doubles with Feliciano Lopez at the Queen's Club in his first competitive event since he underwent a second operation on his right hip in January after the Australian Open, which he had warned could be his last career tournament.
Murray's mother Judy told reporters that the Murray-Williams entry "looks like a really strong partnership."
"It is always difficult to tell in mixed doubles because you only have them in the Grand Slams, so nobody gets the chance to specialize in it or play it a lot.
"But they have both got form in singles and doubles, so hopefully they can be the perfect match."
Given the possibility that Murray and his brother Jamie could meet in men's doubles third round, Judy admitted that the match would torture for her to watch.
"I have been fortunate that Andy's career has been in singles and Jamie's in doubles, so for family harmony it has been great," she explained. "But if it happens I will go to the pub, and wait for a text."
( With inputs from IANS )