Johnson was signed by the Steelers on Tuesday, Dale Lolley of the Observer-Reporter of Washington reports.
Johnson, entering his eighth season in the league, will return to Pittsburgh after spending the last two seasons with the Chargers. In the past two seasons he has only recorded two receptions for a total of eight yards but will battle with Ladarius Green, Matt Spaeth, and Jesse James, among others, for playing time at tight end with longtime veteran Heath Miller retiring earlier in the offseason.