Foster, 29, spent last season on loan at the Hawthorns following his parent club’s relegation to the Championship, making 31 appearances in all competitions.
He has now joined West Brom on a fulltime basis, signing a three-year contract, with an option to extend for a further two years.
Upon the confirmation of the move, Foster tweeted: “Really happy to have just signed for West Bromwich Albion, thx to the fans for making me feel so welcome last year, can’t wait to get started.”
Foster was voted by supporters and players as the best performer last campaign, and new manager Steve Clarke has stressed the value of the signing to the rest of the West Brom squad.
Clarke, who has taken over following Roy Hodgson’s appointment as England manager in May, told the club’s official website: “Ben’s been a priority signing all summer.”
“His performances last season were exceptional and it was important for the club to strike a permanent deal for him.
“It’s a great signing for me and an even better one for the club. I think the supporters will be delighted we’ve been able to keep him on board – and make him our player.
“In any league in the world you want a goalkeeper that is going to make match-winning saves, turn draws into wins and defeats into draws.
“A quality goalkeeper is worth ten or 12 points a season to you – and that’s certainly what we think we’ve got in Ben Foster.”
Foster kept 10 clean sheets last season, which equalled the club’s record for a Premier League season.