Rivers, 28, is a former first-round pick of the Cincinnati Bengals back in 2008. He spent five years with the Bengals before was traded to the Giants in return for a 2012 fifth-round pick that ultimately became S George Iloka.
He was entering the final year of his contract and would have made a base salary of $1.6 million in 2015.
Releasing Rivers will free up $1.7 million in available cap space for the Bills, according to OverTheCap.com.
Last year, Rivers appeared in 12 games for the Bills and recorded 16 tackles. Pro Football Focus has him down for playing 192 snaps to go with a below average rating.