Joiner replaces Hall of Famer James Lofton, who was fired Tuesday after six seasons. Lofton had one year remaining on his contract.
Joiner played 11 seasons in San Diego (1976-86) and finished his career as the team's all-time leader with 586 career catches.
Immediately after his retirement, Joiner was named the Chargers' wide receivers coach. He served in the same capacity with the Buffalo Bills from 1992-2000. His most recent coaching stop was with the Kansas City Chiefs, spending seven seasons (2001-07) as their wide receivers coach before being fired by Herm Edwards three weeks ago.