Legursky, who can play center and guard, visited the Bills on Tuesday, and the five-year veteran agreed to a deal on Wednesday.
Legursky, 26, spent his first four NFL seasons in Pittsburgh, and appeared in all 16 games for the Steelers in 2012. He has played in 50 NFL games with 17 starts.
He will be in the mix for the starting left guard position for the Bills, a race that also includes Colin Brown, Zach Chibane, Chris Scott, Thomas Welch and Sam Young. Legursky could also push David Snow for the backup center role behind Eric Wood.
To make room for Legursky on the roster, Buffalo released linebacker Greg Lloyd.