The Dolphins also received the Steelers' 2020 fifth-round pick and a sixth-rounder in 2021. In turn, the Steelers received Miami's 2020 fourth-round pick and a seventh-round pick in 2021.
"We are very excited to add Minkah to our defense," Steelers general manager and vice president Kevin Colbert said in a statement. "We had him rated very high during the 2018 NFL draft process and we thought that he could be an impact player in this league."
The Steelers placed safety Sean Davis on injured reserve in a corresponding move when adding Fitzpatrick to their active roster. They also signed quarterback Paxton Lynch to their practice squad.
Fitzpatrick, the No. 11 overall draft pick in 2018, received permission to seek a trade from the woeful Dolphins (0-2) earlier in the week because he was unhappy with playing multiple positions, sources told ESPN.
He declined to talk about a potential trade when asked about it prior to Miami's 43-0 Week 2 loss to the New England Patriots.
"I can't focus on this trade, and this and that," Fitzpatrick told reporters Friday. "I'm focused on Sunday. I've got to focus on the New England Patriots."
Fitzpatrick allowed a completion percentage of 49 percent when he was the nearest defender in coverage during his rookie season, according to NextGen Stats. He was ranked sixth among defensive backs with 400 coverage snaps.
The Alabama product brings a valuable contract with him, entering the second year of his rookie deal. He carries a salary of $1.8 million this year, followed by salaries of $1.9 million and $2.7 million, plus a fifth-year option in 2022.
Fitzpatrick will face his former team when the Dolphins travel to Pittsburgh in Week 8 for Monday Night Football.
The Steelers' 2020 pick has a 29 percent chance to be among the top five and a 62% chance to be in the top 10, according to ESPN's Football Power Index.
The Dolphins continued to stockpile picks with the trade. They now have three first-round picks and two second-rounders in 2020. They also have two first-rounders and two second-rounders in 2021.
The trade caps a significant day for the Steelers, after coach Mike Tomlin announced quarterback Ben Roethlisberger was having surgery after suffering a season-ending elbow injury.