Kyrgios, 26, had tweeted on Tuesday implying he would be involved with the mixed doubles and confirmed his partner as Williams when asked during a pre-tournament press conference Saturday.
"The mixed doubles pair of the tournament," he said.
Williams is a two-time mixed doubles winner at Grand Slams, having won titles at the Australian Open and Roland Garros in 1998.
Kyrgios, however, has never gone beyond the third round of a doubles tournament at a Grand Slam. His most recent partners were Amanda Anisimova at the 2020 Australian Open and Desirae Krawczyk at Wimbledon in 2019.
In a 2017 interview, Williams mentioned Kyrgios as her dream doubles partner.
As well as competing in the mixed doubles, both will compete in the singles events at the tournament starting on Monday.
Wimbledon marks Kyrgios' return to competitive action after taking a break from the tennis circuit due to the COVID-19 pandemic. He last played in the Australian Open in February 2019.
"I didn't feel at all that I had to play. I didn't feel obligated to play," he said about his decision to return to tennis with Wimbledon.
"I wasn't pushed. I made a decision. When I was home I wasn't looking at any results. I'd go on Twitter and see the odd result here or there. But I was happy without tennis.
"I just feel like I've got a little bit to give, left in the game. I feel like a lot of people wanted me to play. I feel like I'm playing for a lot of people.
"No one's made me play. I didn't feel like I had to play. It's just a decision that I made."