Williams, who signed with Washington as an undrafted free agent following a three-year career at Texas A&M, takes the roster spot of Joseph Randle, who was cut on Tuesday.
Williams, 5-foot-8, 195 pounds, ran for 127 yards and a touchdown on 31 preseason carries. He also caught two passes for 15 yards.
Former Cowboys running game coordinator Bill Callahan is the offensive line coach in Washington and uses a scheme similar to the Cowboys. Williams’ build and style is in line with Lance Dunbar, who suffered a season-ending knee injury Oct. 4 against the New Orleans Saints.
Williams declared early for the draft after rushing for 1,343 yards and 18 touchdowns in three years with the Aggies. He also caught 38 passes for 330 yards and a touchdown and averaged 24.1 yards per kick return.
He is the second Aggies running back on the Cowboys’ roster, joining Christine Michael. Per league rules, the Cowboys have to keep him on the active roster for three weeks. He is the second player the Cowboys have poached from a practice squad, joining defensive end David Irving, who was on the Kansas City Chiefs' practice squad.