Boak is Port Adelaide’s reigning best-and-fairest winner, claiming the 2019 John Cahill Medal after averaging 30 disposals and seven clearances across 21 games.
He won the same honour in 2011, while he was All-Australian in 2013 and 2014.
Taken at pick No.5 in the 2006 AFL draft, Boak has played 264 games for Port Adelaide, and captained the club between 2013 and 2018.
“The way Travis prepares himself is an inspiration to those around him. He is the ultimate professional,” Power general manager of football Chris Davies said.
“He had a wonderful 2019 season and is in great shape to attack this coming season.
“Having someone of his quality as both a player and person will be important in our success.”