Carrington, 27, returns to the Bills after previously spending four seasons (2010-2013) with the team. He spent last season with the St. Louis Rams, playing in eight games as a reserve.
The Bills were in need of depth along their defensive line after not drafting a defensive lineman last week. Carrington will compete with Stefan Charles, Corbin Bryant and Jarius Wynn for a starting role alongside Kyle Williams and Marcell Dareus in the Bills' base defense.
By signing Carrington before the NFL's May 12 cut-off date for unrestricted free agency, the Bills will most likely not receive a 2016 sixth-round compensatory draft selection they were set to earn had they not signed Carrington. OverTheCap.com now projects the Bills to earn only one sixth-round compensatory choice, which are awarded by the NFL based on how many unrestricted free agents a team loses compared to how many they sign.
Carrington started the first three games of the 2013 season for the Bills in Mike Pettine's defense, which is based on Rex Ryan's scheme, before suffering a season-ending quad injury.