The pair will officially enter the draw on Wednesday morning before the 11 a.m. deadline.
Per the email from Matt Gentry, they wanted to wait to announce until after Williams' first-round win earlier on Tuesday. She won, 6-2, 7-5, against Giulia Gatto-Monticone. Williams, a 23-time Grand Slam singles champion who has struggled with injury for much of 2019, was elusive about the potential partnership with Murray during her news conference after her victory.
"This is crazy," she said. "I don't know. I'm still kind of in the singles mode, trying to figure that part out. We'll see. I could use extra matches, though, so... Could be something."
Later a reporter asked her for a percentage in regards to how likely it was she would play with him.
"If you guys really want it, then maybe I'll do it," the 37-year-old said in response.
Murray, a beloved figure in his native Great Britain, made his return to competition last month following a second hip surgery after a second-round loss at the Australian Open. The three-time Grand Slam singles champion, including two at Wimbledon, is not playing in the singles draw, but begins doubles play on Thursday with Pierre-Hugues Herbert.
Williams won the Wimbledon mixed doubles title in 1998 with Max Mirnyi, as well as the US Open event the same year. Murray has played just once in a mixed doubles draw, losing in the second round in 2006 with partner Kirsten Flipkens.
Murray, 32, made headlines last week after revealing he was having trouble finding a mixed doubles partner to play with at the All England Club. World No. 1 and French Open champion Ashleigh Barty was among one of several women's players to turn him down. She called it "the hardest decision" she ever had to make in declining his offer.
The official mixed doubles draw will be announced on Wednesday at 2 p.m. local time with play beginning later in the week.
Simon Cambers contributed to this report.