Gilliam agreed to a three-year contract worth up to $12 million with the Patriots on Monday, Mike Garafolo of NFL Network reports.
Gilliam's deal, which can be made official Wednesday at the start of the new league year, includes $6 million in guaranteed money and a salary of $4.4 million in the first year. The fullback spent the previous six seasons with the NFC East rival Bills, compiling 16 catches for 135 yards and two touchdowns, as well as eight carries for 14 yards, in 94 regular-season appearances.