Jackson was drafted in the first round with the 24th overall pick in the 2004 NFL Draft by the St. Louis Rams. He was the first running back to be selected that year. The Rams traded picks with the Denver Broncos and Cincinnati Bengals to get Jackson. Denver traded Deltha O'Neal to Cincinnati for their first round pick. Then, St. Louis traded up to Cincinnati's selection to grab Jackson while the Bengals chose Chris Perry to replace the departed Corey Dillon, who was traded to the New England Patriots.