Darby played his college ball at the
University of Alabama. In 2002, he redshirted as a freshman. He first saw action his freshman year in 2003 under former coach
Mike Shula. He played sparingly behind former running backs
Shaud Williams and Ray Hudson. He had 185 yards on 34 carries (5.4 avg.) and also caught three passes in the 10 games he played (one start). With the graduation of Shaud Williams and starter Ray Hudson falling to injury, Darby saw extensive action in 2004. Taking over the starting running back job five games into the season, Darby rushed for over 1,100 yards. Due an injury at the end of the season, Darby was unable to play in the
Music City Bowl. The Tide finished with a 6–6 record. Darby was a Second-team All-SEC selection after playing 12 games with five starts. He logged 219 carries for 1,062 yards (4.8 avg.) and a career-high eight touchdowns and had 15 receptions for 74 yards (4.9 avg.) and one score. Darby entered 2005 as a preseason All-SEC player and finished the season as one of the top running backs in the SEC. That year, the Crimson Tide finished 10-2 with a victory over
Texas Tech in the
Cotton Bowl Classic. He was a First-team All-SEC after starting all 12 games, with 239 carries for a career-high 1,242 yards (5.2 avg.) and three touchdowns and had 29 catches for 132 yards (4.6 avg.). Darby entered his senior season needing just over 1,000 yards rushing to surpass
Shaun Alexander as Alabama's career rushing leader. He rushed for over 800 yards and finished the season without a rushing touchdown. The Crimson Tide finished 6-6 with a loss to
Oklahoma State in the
Independence Bowl. In 2006 Darby was a Second-team All-SEC selection by The NFL Draft Report. He started all 13 games carrying 210 times for 835 yards (4.0 avg.) and caught 23 passes for 130 yards (5.7 avg.) and one score. After the season, Darby was selected to play in the
Senior Bowl. ==Professional career==