The Buffalo Bills pulled off the biggest free-agent acquisition in franchise history by agreeing to a contract with two-time Pro Bowl defensive end Mario Williams that gives their pass rush a significant boost.

Terms of the contract were not disclosed but media said the deal would make Williams, 27, the highest-paid defensive player in the National Football League (NFL).

Williams, regarded as one of the top free agents available, was drafted first overall in 2006 by the Houston Texans and would be counted on to bolster a Bills defence that managed just 29 sacks last season.

His signing gave Buffalo their most accomplished pass rusher since Pro Football Hall of Famer Bruce Smith, who left the team in 2000 as the franchise and NFL all-time sacks leader.

The Bills, who finished 6-10 in the 2011 campaign and missed the playoffs for the 12th straight year, entered the offseason intent on bolstering their pass rush.

Williams, who was limited to five games last season due to a torn chest muscle, has 53 sacks and 241 tackles in 82 career games during six NFL seasons with the Texans.

(Reporting by Frank Pingue in Toronto; editing by Julian Linden)