Hillis has been without a team since being released by the Tampa Bay Buccaneers last month and will give the Giants cover at running back following a number of injuries to players in that position.
Starting running back David Wilson has been ruled out for at least three or four weeks with a neck injury, while Brandon Jacobs is nursing a hamstring injury and Andre Brown is unable to return until week 10 at the earliest having broken his leg during pre-season.
Hillis has plenty of experience in the NFL having spent time at the Denver Broncos and Kansas City Chiefs as well as the Browns, with his best season coming in Cleveland three years ago when he rushed for 1,117 yards and 11 touchdowns.
He has been unable to replicate that form since, however, and could still find himself behind rookie Michael Cox in the Giants' pecking order should Jacobs not be fit for next Monday's match against the Minnesota Vikings.
Da'Rel Scott, who picked up a hamstring injury in the Giants' last match, was released to make room on the roster for Hillis.