The Lions had a vacancy on their roster after starting middle linebacker Stephen Tulloch was placed on injured reserve with a torn anterior cruciate ligament.
Bynes had been on the Ravens' practice squad after being cut earlier this month. The 6-foot-1, 240-pounder is known for his physical style.
Bynes has played in 26 career games with nine starts and was on the Ravens' practice squad in 2011 and 2012. He started six games last season at inside linebacker and played in all but one game as he recorded 45 tackles and three pass deflections.