Buffalo announced the signing Sunday. The Bills released guard Vladimir Ducasse in a corresponding transaction. Chicago released Acho in March.
"Could not be more grateful," Acho tweeted. "God is closer than we know."
Acho, 30, had one tackle in four games last season for Chicago before landing on injured reserve with a torn pectoral. The eight-year veteran will likely serve as a depth linebacker for the Bills.
The fourth-round pick in the 2011 NFL Draft played his first four seasons with the Arizona Cardinals. He joined the Bears in 2015. Acho had a career-high 48 tackles and six tackles for a loss during his 2012 campaign. He also recorded four sacks, three passes defensed, two forced fumbles and two interceptions in his second season with the Cardinals.
Acho had a career-high 18 quarterback hits in 16 games during his 2017 campaign with Chicago. He had a career-high seven sacks during his rookie season with the Cardinals.
He was the Bears' Walter Payton Man of the Year nominee in 2016 and 2017. The Dallas native played at the University of Texas before entering the NFL.
The Bills had Matt Milano, Tremaine Edmunds, Lorenzo Alexander, Maurice Alexander, Julian Stanford, Corey Thompson, Vosean Joseph, Tyrel Dodson and Deon Lacey listed at linebacker on their first unofficial depth chart for the 2019 season.