The Dolphins announced the deal Tuesday night on the first day of NFL free agency. Martin's move cross country brings him back to the Bay Area to be reunited with his former Stanford coach, Jim Harbaugh.
An investigation for the NFL determined last month that Dolphins guard Richie Incognito and two other offensive linemen engaged in persistent harassment of Martin, another offensive lineman and an assistant trainer.
The trade capped a busy first day for the 49ers, who lost to the Super Bowl champion Seattle Seahawks in the NFC championship game.
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