Terms of the contract, which was announced by the team on Thursday, were not yet available. The Mack deal had been brewing since the wee hours of Wednesday morning after left tackle Trent Williams tagged Mack in an Instagram post announcing his own re-signing with the 49ers.
Long before that, however, Mack to San Francisco had been a logical connection. He played his college ball at nearby Cal and was a favorite of 49ers coach Kyle Shanahan when he played for him with the Cleveland Browns in 2014 and the Atlanta Falcons in 2016.
Mack, 35, completed his fifth season with the Falcons last season. He joined Atlanta as a free agent on a five-year, $57.5 million contract before the 2015-16 season.
He has been selected to six Pro Bowls in his 12-season career, including his first three seasons with the Falcons.
Mack spent the first seven seasons of his career in Cleveland, where he was selected to his first three Pro Bowls.
Drafted with the No. 21 overall pick in 2009 by the Browns, he has started all 179 games in his career. He missed only two games for the Falcons in his five seasons, both coming last season, as he missed the final two games because of a concussion and being placed on the reserve/COVID-19 list.