ORCHARD PARK, N.Y. -- New England quarterback Tom Brady might want to watch his back. The Jets' Mark Sanchez, too.

After spending the past six seasons harassing quarterbacks for the Houston Texans, defensive end Mario Williams -- one of the NFL's top pass-rushers -- has found new motivation in a whopping contract and a new home in the AFC East with the Buffalo Bills.

"I'm ecstatic, very excited. I can't wait for the opportunity," Williams said Thursday after signing a six-year deal potentially worth $100 million. "There's no pressure. I've played against great quarterbacks. And I'm looking forward to playing against these quarterbacks, chasing them down and making things happen."

Williams' deal, which includes $50 million in guaranteed money, is the richest ever given to an NFL defensive player. It came after two days of talks, which started when the Bills flew the former top draft pick to Buffalo on a private jet Tuesday, shortly after the NFL's free-agency period opened.

Terms of Williams' contract were provided by the player's agent, Ben Dogra.

"We got a lot better," Buffalo general manager Buddy Nix said, noting the Bills addressed their highest offseason priority by bolstering what had been an anemic pass rush. "Good things come to the people that wait. So you guys have been waiting, and we've got a good thing here."

Though the contract was agreed to shortly after noon, the news conference to introduce Williams was delayed by more than two hours as the two sides worked out the final details.

The wait was even longer for Nix, who noted the Bills' pro scouts identified Williams as their key target since January.

"The No. 1 guy for us from Day 1 was this guy," Nix said. "Obviously, you don't do anything until he hits free agency, but it's been a long process. And it's been fun, especially since it turned out right."

After quarterback Peyton Manning, Williams has been regarded as one of the top free agents available this offseason.