Dareus was the third overall pick in 2011 and has started 35 games over his first three seasons. He posted career highs in tackles (71) and sacks (7.5).
However, Dareus ran into trouble with first-year coach Doug Marrone last season. He was held out from starting each of the Bills' final two games for violating a team rule.
Under the rules of the collective bargaining agreement, the Bills had the right to exercise his option for the 2015 season at $8.06 million. It becomes guaranteed at the start of the 2015 league year.
The Bills had until May 3 to exercise Dareus' option.
Information from The Associated Press was used in this report.