The Northern Ireland international has ended his time at Old Trafford and is now looking to start a new journey with West Brom.
The club has announced the signing on an undisclosed fee.
Evans had undergone a medical at the Baggies’ training ground on Friday and now becomes their fifth new recruit of the summer.
“I hope to push the Albion up the League,” the centre-back told his new club’s official website.
“It’s a new, fresh challenge for me, one I’m looking forward to. I know a few of the lads already and I spoke to a couple, who highly recommended the club.”
Evans’s Manchester United career comes to an end just shy of making 200 appearances for the club in all competitions, his 18 games last season taking him to a total of 198.