Lynch was added to the Steelers' 53-man roster from the practice squad Friday.
The 2016 first-rounder spent the preseason with the Seahawks but was let go at September's roster deadline and joined the Steelers' practice squad Sept. 17. Lynch provides some additional depth at quarterback with Ben Roethlisberger (elbow) on injured reserve and Mason Rudolph dealing with a concussion. Lynch will serve as the No. 2 quarterback behind Devlin Hodges this week against the Chargers with Rudolph sidelined.