Williams is the newest member of the Arizona Cardinals.
The move comes only two years after the Cardinals used a first-round selection on Beanie Wells.
As a rookie, Wells rushed for 793 yards. Last year, appearing in 13 games with two starts, Wells rushed only 397 yards, averaging 3.4 yards per carry.
Williams set the single-season Virginia Tech rushing record in 2009, with 1,655 yards. Last year, a hamstring injury and a running-back rotation kept Williams under 500 yards.