Pettine, whose contract had expired with the Jets, agreed to a three-year deal with Buffalo to work on new coach Doug Marrone's staff.
Nathaniel Hackett, who was Marrone's offensive coordinator at Syracuse, will also be his offensive coordinator with the Bills, the Buffalo News reported.
Jets secondary coach Dennis Thurman is expected to be named the team's defensive coordinator in place of Pettine, league sources told ESPNNewYork.com on Tuesday.
Thurman is the natural successor, as he has worked with Jets coach Rex Ryan longer than any of the other defensive coaches on the staff. Ryan said he will wait until the next general manager is hired before making anything official.
Pettine served as Ryan's coordinator for four seasons, but he turned down a contract extension early in the season. Money was an issue, but Pettine also might want to escape Ryan’s shadow.
"We had conversations and, right now, Mike thinks it’s best that he goes to a different team as a defensive coordinator, and I wish him all the best -- unless he goes to Buffalo," Ryan joked Tuesday.
ESPN senior NFL analyst Chris Mortensen and ESPNNewYork.com's Rich Cimini contributed to this report.