The Cowboys signed Collins to a one-year deal.
Collins, 29, played in every game last season for the Lions, with two starts, following a three-year run with the New Orleans Saints. He had eight carries for 19 yards and five catches for 39 yards and a touchdown last season.
Tyler Clutts, 30, has been the Cowboys’ fullback for the past 20 games and is also a free agent. He had one catch for 1 yard in the regular season and caught his first touchdown pass in the playoff loss to the Green Bay Packers.
The Cowboys have not had a big role for a fullback in the past several years, preferring to go with two tight ends instead of the traditional two-back set.