Trengove played 153 games for the Power, including 19 this season, since being recruited with pick No.22 in the 2008 National Draft.
He won Port’s best and fairest award in 2011.
But after losing his spot in the side late in the season, Trengove decided it was time for a fresh start, signing a three-year deal at the Kennel.
“Obviously it’s a big change after so long at Port Adelaide but coming back home I’m going to be around family and friends and I’m really excited about the football club and what the future holds,” he said.
“I just see the Bulldogs as the perfect fit for me. I think I can add a lot to the group and I think we’ll be back up and hopefully playing finals again next year.”
Bulldogs list manager Jason McCartney said the club is looking forward to utilising Trengove’s versatility.
“Obviously the role he can play; he’s played a lot of footy as a key defender and he’s shown the capability to perform a different role in the ruck,” he said.
“So we’re excited by the versatility, but he’s such a great club person, he’s got good leadership qualities and he’s extremely competitive and that’s going to really complement our group as well.”
Port Adelaide has received a round two compensation pick, currently pick No.30 in this year’s National Draft as compensation from the AFL for losing Trengove to free agency.