"We are pleased to have reached an agreement with the Ravens for Bryant," Dolphins general manager Jeff Ireland said. "He is a proven and experienced player who will be a great addition to the offensive line."
Ravens coach John Harbaugh was confident the trade, which is for a conditional late-round draft pick, would get done.
"It's a good move for us. It's a good move for Bryant," he said.
The Dolphins released linebacker Josh Kaddu to create a roster spot for McKinnie.
The Dolphins' offensive line has struggled this season, allowing 26 sacks in the first six games.
Right tackle Tyson Clabo has allowed a team-high eight sacks, including two in Sunday's loss to the Buffalo Bills. Clabo was put on notice by Miami's coaching staff before the bye, and now the McKinnie trade puts Clabo's job status in question.
McKinnie, who started at left tackle during the Ravens' Super Bowl run last season, had lost his starting spot to Eugene Monroe, who was acquired by Baltimore in a trade with the Jacksonville Jaguars.
He has been inactive the past two games after starting the first five games at left tackle. In his last start, in a 26-23 Ravens victory against the Dolphins, he allowed two hits and four hurries. He nearly cost the Ravens the game by letting rookie Dion Jordan hit quarterback Joe Flacco from behind, which led to an interception return for a touchdown in the fourth quarter.
McKinnie signed a two-year, $7 million contract with Baltimore this offseason.
ESPN.com Ravens reporter Jamison Hensley contributed to this report and ESPN.com Dolphins reporter James Walker contributed to this report.