Essex, an unrestricted free agent, spent the first six seasons of his career with the Steelers. He started five games in 2010 for the defending AFC champions.
The signing bolsters the depth along Pittsburgh's injury-riddled offensive line. Tackles Jonathan Scott and Marcus Gilbert both sustained minor injuries during the team's 24-14 exhibition win over Philadelphia last week.
The Steelers waived rookie guard Nevin McCaskill to make room on the roster for Essex.