Pittsburgh is in need of a new backup quarterback following the season-ending injury to Ben Roethlisberger.
Former backup Mason Rudolph is now the starter and the only other quarterback on the roster is former practice squad passer Devlin Hodges.
Lynch, 25, was taken with the No. 26 overall pick after the Broncos traded up from No. 31 overall to get him in 2016 NFL Draft. Lynch signed a four-year, $9.4 million contract that includes $7.88 guaranteed and was set to make a base salary of $1.31 million in 2018 when the Broncos waived him coming out of the preseason.
After interest from a number of teams, Lynch signed a futures deal with the Seahawks for the 2019 season. Seattle waived Lynch coming out of the preseason this year.
In 2017, Lynch appeared in two games for the Broncos and completed 66.7 percent of his passes to go along with two touchdowns and three interceptions. He also rushed for 30 yards.