The 33-year-old singer will act as advisor to Team Pharrell on season seven. Stevie Nicks will mentor Team Adam Levine, Little Big Town will advise Team Blake Shelton and new coach Gwen Stefani has recruited husband Gavin Rossdale to fill the role on her team. The season will mark Williams and Stefani's debut as judges.
Williams and Keys previously collaborated on "It's On Again" for the Amazing Spider-Man 2 soundtrack, and duet "Know Who You Are." The musicians are both managed by Ron Laffitte; Keys "parted ways amicably" with manager Will Botwin this week. She last released Girl on Fire, her fifth studio album, in 2012.
Season seven of The Voice premieres September 22 on NBC. Shelton has coached three contestants to victory thus far; Team Adam Levine has won twice and Team Usher once.