The 33-year-old has made 35 Premier League appearances for Steve Clarke's side this season and has committed to a new two-year contract
The 33-year-old, who has been at the Hawthorns since July 2011, has made 35 Premier League appearances for Steve Clarke's side and formed a solid centre-back partnership with Jonas Olsson this season.
For his performances this term, McAuley was also voted West Brom's Player of the Year by his team-mates and supporters.
"I'm absolutely delighted the deal has been done," Clarke told the club's official website.
"The fact Gareth has signed it tells you it is a good deal for him - and it is certainly a good deal for the club. He's been a standout performer this season and deserves every reward he gets.
"Gareth's important to the dressing room. I've mentioned a number of times how strong the dressing room is and how we have a lot of good characters in the dressing room. Gareth is one of those.
"He's important to the club and squad - both on and off the pitch."