Priddis joined fellow midfielder Luke Shuey in extending his contract with the Eagles.
Priddis, 29, began with West Coast as a rookie in 2006 and is now the team's most experienced player, with 173 matches to his credit.
"[The contract] means I'm going to be a one-club player with the club that gave me an opportunity that I was so grateful for," the 2014 Brownlow winner told the club website.
"I was pretty desperate to get on an AFL list, and this takes me to 11 years at the footy club, which is something I'm very proud of."
Shuey has extended his contract until the end of 2018.
The 24-year-old finished third in the Eagles' best-and-fairest award this season.
"I think we've had our opportunities over the last three or four years and we've probably under-delivered, so I think we owe the footy club some success," Shuey said.
"We've got the right squad for it, and as players, I think we all need to go to another level for that to happen.
"It's going to be an exciting summer this year, going into 2015. It's going to be a hard pre-season for sure, but we're looking forward to putting in the work and improving."
