Gildon was cut in June by the Steelers after he recorded his lowest total in six seasons with a half dozen. Before last season, he posted nine sacks in 2002, 12 in 2001 and 13.5 in 2000.
The 6-4, 250-pound linebacker was drafted in the third round of the 1994 draft out of Oklahoma State. He has been a starter since 1996 and was the team's defensive captain. Gildon, who turns 32 on July 31, has 77 career sacks and made the last three Pro Bowls.
The Bills' deal for Gildon is believed to be worth between $1 million and $1.5 million, with a signing bonus of about $500,000, according to the Buffalo News.
Other teams on Gildon's trail included the Cincinnati Bengals.