Reed's agent, Mike McCartney, announced the move on Twitter. The Steelers swapped a 2023 sixth-round draft pick for the outside linebacker and a seventh-round pick from the Broncos, a source confirmed to ESPN.
The Steelers needed to shore up depth at the position with a lingering ribs injury to Alex Highsmith, though defensive coordinator Teryl Austin said Highsmith hasn't had any setbacks in his recovery. Reed likely rounds out the group that also features reigning Defensive Player of the Year T.J. Watt and backup linebacker Derrek Tuszka.
"Those guys can't play every snap with the way they play, the physicality in which they play," Austin said. "You have to have a third guy and a lot of times we'll get a fourth guy to maybe get 10 snaps of game.
"It's important to have depth especially at that position because at the end of games, when you need somebody to rush the passer and try to end the game, those are the guys that get it done."
Reed, who originally made the Broncos' roster as an undrafted rookie in 2019, has been one of the most popular players for the Broncos, both in the locker room and in the community.
But the Broncos moved inside linebacker Baron Browning to outside linebacker this offseason and then signed Randy Gregory to a five-year, $70 million deal in free agency, leaving no room for Reed to squeeze his way on to the depth chart.
For the Broncos, Reed has been the guy to solve a problem in recent seasons. When Von Miller suffered a season-ending ankle injury in 2020, Reed started 13 games and finished with a team-leading eight sacks.
And last season, when Bradley Chubb missed 10 games due to ankle surgeries, Reed started 13 games and finished with five sacks.
ESPN's Jeff Legwold contributed to this report.