The 32-year-old is Albion’s fourth longest-serving current player after Chris Brunt, James Morrison and Jonas Olsson and his new deal will keep him at the club until the summer of 2017.
Myhill enjoyed an extended run in Albion’s first team during the 2014/15 season after Ben Foster suffered a knee injury.
In all he played 11 Premier League games last term, keeping four clean sheets along the way – including a brilliant performance in the 1-0 win at Manchester United, where he saved Robin van Persie’s penalty.
Myhill said: “It’s great to get my future sorted out. It’s never easy being a goalkeeper when you’re not in the team but the Premier League is the place you want to be in.
“I enjoyed the final few months of the season and tried to do my best during that period.
“Pre-season has been tough but now we are beginning to focus on making sure we are ready for that opening game of the season.”
Head coach Tony Pulis said: “I’m delighted Boaz has signed his new deal.
“He had a smashing end to the season when he came into the side and has worked very hard throughout the summer.”