He becomes the second notable veteran defensive player added by the Steelers in free agency, joining former Kansas City Chiefs cornerback Steven Nelson, who signed a three-year contract with Pittsburgh. The Steelers also signed wide receiver Donte Moncrief to a two-year deal.
Barron, who was the Rams' starting inside linebacker, was released by the team earlier this month with two years remaining on his contract.
He was sidelined four games to start the 2018 season because of a nagging ankle injury and finished with 43 tackles (the lowest total of his career), a sack and a forced fumble.
The Rams acquired Barron midway through the 2014 season from the Tampa Bay Buccaneers, who selected him with the seventh overall pick in the 2012 draft.
The Rams moved Barron from safety to linebacker during the 2015 season and he finished with 113 tackles, five pass deflections and three forced fumbles.
Barron, 29, finished 2016 ranked second on the team with 118 tackles, two interceptions and a sack as the Rams stumbled to a 4-12 finish.
Over the past two seasons, Barron has been slowed because of various injuries but also played an instrumental role in helping the team win back-to-back division titles and earn its first Super Bowl appearance since the 2001 season.
A seven-year veteran, Barron has 628 career tackles, nine sacks, six forced fumbles, three fumble recoveries and eight interceptions.