The Dockers receive picks 40 and 82 in return, while the Dogs also receive a future fourth round pick from Fremantle.
Crozier, 23, has played 69 games in six seasons with the Dockers. He had his best season this year, playing 19 matches and kicking 13 goals.
“It was a dream come true for me to come over here and play for the Dockers and now it’s time for me to move back with family and friends and I’m looking forward to the opportunity with the Western Bulldogs,” Crozier said.
Bulldogs list manager Jason McCartney said the Dogs see Crozier as playing more down back in 2018 rather than up forward where he was primarily used this season under Ross Lyon.
“Hayden’s got a great athletic profile, which will allow us the flexibility to play him back, forward or wing, with his aerial game a particular strength,” McCartney told the club’s website.
“We see him primarily at half-back which, with the retirements of Bob Murphy and Matthew Boyd this season, will help our defence transition in 2018 and beyond.
“It’s a great result, securing Fremantle’s future fourth-round pick enables us flexibility around draft value index points in the future.”