It's not immediately known what role Johnson will fill on the Bills' staff, but he is expected to work under defensive coordinator Jim Schwartz, who was hired last week.
The Bills are without both of their linebackers coaches from last season. Outside linebackers coach Jim O'Neil became the defensive coordinator of the Cleveland Browns, while inside linebackers coach Chuck Driesbach was fired. The Bills have also granted the Browns permission to interview defensive line coach Anthony Weaver.
Johnson, 49, spent the past 14 seasons as an assistant coach for the Patriots, serving as an assistant linebackers coach (2000), inside linebackers coach (2001-2003), defensive line coach (2004-2011), and linebackers coach (2012-2013). He decided to leave the team earlier this month.
Patriots coach Bill Belichick said in a statement that he was "proud and honored to have spent more years of my career with Pepper Johnson than any other player or coach." Johnson played under Belichick as a linebacker with the New York Giants (1986-92), Cleveland Browns (1993-95) and New York Jets (1997-98).
Schwartz served as a personnel scout for the Browns from 1993-95.
It is believed that Johnson departed the Patriots to seek opportunities for advancement. Schwartz, a veteran coach who was fired after five seasons with the Detroit Lions, could be in line for another head coaching job as soon as the 2015 season. That could potentially open the door for Johnson to become the Bills' defensive coordinator.