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.
Though it didn't work out with Jay Cutler this season, Trestman helped the Bears become the NFL's second-highest scoring team in 2013 with Cutler and Josh McCown at quarterback.
Ravens Hire Trestman As Offensive Coordinator
John Clayton breaks down why Marc Trestman stepping in as the Ravens' new offensive coordinator will be a good fit for Joe Flacco.