The Steelers are also giving up a fifth-round selection in 2020 and a sixth-rounder in 2021, while getting the Dolphins' fourth-round pick in 2020 and a seventh-rounder in 2021.
Fitzpatrick, the 11th overall pick of the 2018 draft, had grown unhappy with his usage in the Dolphins' defense. The team allowed the defensive back to seek a trade.
"We are very excited to add Minkah to our defense," Steelers general manager Kevin Colbert said Tuesday in a release. "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 rebuilding Dolphins are focusing on the future and now hold three first-round picks in the 2020 draft. Miami acquired the Houston Texans' first-rounder in an August trade that sent star left tackle Laremy Tunsil and receiver Kenny Stills packing.
Meanwhile, the Steelers get a 22-year-old star who can play safety, linebacker, or slot corner. Fitzpatrick is signed through 2021 on his four-year, $16.4-million rookie deal, and he's also eligible for a fifth-year option.
The first-round pick that Pittsburgh sent to Miami could end up being valuable, as the Steelers have started this year 0-2 and lost quarterback Ben Roethlisberger to a season-ending injury.