Tollefson was a member of both the Packers and Raiders practice squads, after not sticking on the 53 man roster for either team in 2006 and entering 2007 with the Raiders.
In October of 2007, the Giants signed Tollefson from the Raiders practice squad. Tollefson would make his NFL regular season debut with New York that season, seeing action in six games, and getting credit for two tackles and two assists.
While he was not a starter for the majority of his career with New York, he certainly made his presence felt with the team. In five regular seasons as a Giant, Tollefson picked up 56 tackles and 25 assists. He also had ten sacks and five passes defended.