Trestman, 59, joins the Ravens after going 13-19 in two seasons with the Bears. He replaces Gary Kubiak, who was announced as the Denver Broncos' new coach Tuesday.
This is the Ravens' fourth new offensive coordinator in as many seasons.
Trestman interviewed for the Tampa Bay Buccaneers' offensive coordinator position earlier this offseason. He has been an offensive coordinator for four NFL teams -- the Cleveland Browns, San Francisco 49ers, Arizona Cardinals and Oakland Raiders.