Roman was fired by the Bills just two games into the 2016 season, his second with the club. The 44-year-old also spent the previous four years as the San Francisco 49ers' offensive coordinator and two years with Stanford in 2009-10, working with Baltimore coach John Harbaugh's brother Jim at both stops.
"I am very excited to join the Ravens' staff and help coach (John) Harbaugh and Marty Mornhinweg in any way I can," Roman said. "The building blocks are there for this team, and we're all looking forward to being better. I've been with the Ravens before and know firsthand what a great organization they have. My family and I are happy to be back."
Roman also served as an assistant offensive line coach in Baltimore in 2006 and 2007.
"Greg had other opportunities over the last few days, and we're pleased that he has decided to join the Ravens," John Harbaugh said. "I've known Greg for a long time, and he's a hard worker and very creative. Our football team just got better."
Mornhinweg also sang Roman's praises.
"Getting a veteran coach like Greg Roman to join our staff is a coup for the Ravens," Mornhinweg said. "He is a very sound coach and a good team player who will help us build our offense."
Baltimore also promoted Richard Angulo to assistant offensive line coach after serving as tight ends coach for the past two seasons.