Wannstedt, who spent the last six seasons as head coach at the University of Pittsburgh, will also be in charge of the linebacking position.
"We are extremely pleased to have Dave Wannstedt join our staff," Buffalo Coach Chan Gailey said. "Dave and I have known each other for quite some time.
"I respected him when I worked for him and I'm excited that he is going to be able to join our staff. He'll have the title of assistant head coach and will be coaching the inside linebackers. I look forward to him being able to help our team in many ways."
Wannstedt worked on the coaching staff of Jimmy Johnson at Oklahoma State, the University of Miami and the Dallas Cowboys. After Dallas won the Super Bowl in 1992, Wannstedt put in a six-year tenure as head coach of the Chicago Bears. He worked with Gailey when both were assistants with the Miami Dolphins.