The Hawks gain pick 23 in the draft for the 23-year-old Hill, who played an important role in their 2013, 2014 and 2015 AFL flag-winning teams.
The speedy winger told Hawthorn late in the 2016 season that he wished to return to his home state of Western Australia.
“Bradley informed the club he had a strong desire to return to Western Australia and play with his brother at Fremantle,” Hawks list manager Graham Wright said.
“We have worked closely with his management and Fremantle to facilitate a deal that we feel benefits everyone involved.
“He has been a great servant to this club and leaves a triple premiership player.
“We would like to thank Bradley for his contribution to the Hawthorn Football Club and wish him all the best in the future.”
The move of Fremantle unrestricted free agent Chris Mayne to Collingwood on a four-year deal on Wednesday facilitated the Hill trade.
The Dockers used the compensation pick they received from the AFL (No.23) for the loss of Mayne to secure Hill from the Hawks.
Fremantle have already landed highly-rated forward Cam McCarthy from Greater Western Sydney as they look to climb back up the ladder next season.
“At 23 years of age, Bradley is an experienced premiership player with elite running and skill level,” Dockers list manager Brad Lloyd said.
“We believe he will be a valuable acquisition to our playing list and be a long-term player for Fremantle.”
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