The Black Eyed Peas musician will join Jessie J on the UK version of the hit reality series, which will be hosted by Holly Willoughby and Reggie Yates.
"I'm proud to be doing The Voice UK because the UK was the first place I saw success," said the star. "It's the place I'm the most creative outside of home."
BBC One controller Danny Cohen added: "I am thrilled that will.i.am has signed up to be a coach on The Voice. He is a huge star who will bring a unique creativity to the show."
will.i.am, real name William James Adams Jr, has sold 31 million albums worldwide and won seven Grammy Awards as part of the Black Eyed Peas. He has also collaborated with the likes of Michael Jackson, Rihanna, Usher, Nicki Minaj and Cheryl Cole.
He was first rumoured to be involved with the UK version of The Voice in late October.
The Voice will debut on BBC One in early 2012.
> The Voice pick-up defended by BBC One controller Danny Cohen