The 33-year-old, who was out of contract at the end of the current campaign, has put pen to paper on a new two-and-a-half-year deal which will keep him at The Hawthorns until the summer of 2019.
Foster has been an ever-present for the Baggies this season and recently made his 150th Premier League appearance for the club.
Albion boss Tony Pulis has been pleased with Foster's form this season, keeping three clean sheets as the club head into the Christmas schedule eighth in the table ahead of the Boxing Day trip to Arsenal.
"We're delighted we've extended Ben's contract
His form this season has been there for all to see and he continues to set the standards at the club all the goalkeepers have to aspire to," said Pulis
Foster joined West Brom on loan from Birmingham in 2011 before making the move permanent the following year
He has made 161 appearances for the club in all competitions, keeping 41 clean sheets and follows midfielders Craig Gardner and Claudio Yacob and Pulis himself in committing his future to the club in recent months
Source : PA
Source: PA