Barrass, who was already contracted for 2022, has become a key pillar of West Coast's defensive set-up since making his debut in 2015.
The 26-year-old has combined brilliantly with Jeremy McGovern to form one of the league's best intercept marking duos, and he is on track to notch his 100-game milestone in round one next season.
Barrass would have become a free agent at the end of next season, but the new deal ties him to West Coast until 2027.
"I'm really grateful for the opportunity to play on at this footy club," Barrass said.
"It feels great having some security behind me and knowing that I can focus on building this list going forward, and keeping the environment that's really healthy for improvement.
"I've been really lucky to have played a lot of footy with some really senior guys.
"In the leadership space (we) have really good role models and blokes who prompt you to get the best out of yourself every time you come into the club."
Eagles midfielder Luke Edwards, who is the son of Adelaide Crows great Tyson Edwards, has re-signed for a further two seasons.
Edwards played eight games in his debut season this year, with the highlight being a 27-disposal effort in the round 13 win over Richmond.
West Coast suffered a huge blow earlier this month when All-Australian defender Brad Sheppard was forced to retire at the age of 30 due to concussion.
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