He played college football for the Utah State Aggies and was selected by the Redskins in the third round of the 2004 NFL draft.

In wrestling, he posted a 54–0 record his senior season, winning a Utah state championship and earned All-America honors.

After being used sparingly in the first half of the 2004 season, Cooley began to be used more extensively in the last eight games, developing a rapport with Redskins quarterback Patrick Ramsey.

He was the Redskins' nominee for the NFL Man of the Year award[4] for his work reading to children and feeding the poor.

In the sixth week, Cooley had nine receptions for a career-high 105 yards and one touchdown in a 17–14 loss against the Green Bay Packers.

On December 18, he was named to the 2007 Pro Bowl team with Redskins tackle Chris Samuels, long-snapper Ethan Albright, and the late safety Sean Taylor.

In Week 5, he had eight receptions for a career-high 109 yards and one touchdown, on a pass from Antwaan Randle El in a 23–17 win against the Philadelphia Eagles.

On October 27, 2009, Cooley commented via Twitter that the break may not have been as bad as originally thought and that he could possibly return in as little as four weeks.

[13] In Week 3 against the Dallas Cowboys, Cooley subbed in for Darrel Young and Mike Sellers, who were both injured, and played the fullback position for the first time in his career.

[15] On October 25, 2011, Cooley was placed on injured reserve after his knee was examined further by his doctor and he was told that it would take another four or five weeks before full recovery.

[16] During the preseason, it was reported that Cooley's knee was completely healed from the surgery and that he even lost 20 pounds to prepare for the 2012 season.

[19][20][21] On October 21, 2012, Cooley agreed to re-sign with the Redskins after Fred Davis tore his Achilles tendon and was done for the season.

On August 11, 2015, it was reported that Cooley expressed interest into returning to the NFL after working out at the Redskins facility during the off season.

[41] Cooley, frequently referred to by his nickname "Captain Chaos," is known for his eccentric hair styles, affinity for heavy metal music, and what one reporter has called an "Animal House persona".

On Sunday, September 14, 2008, Cooley posted on his blog a photo of Redskins training materials that also included his genitals.

Cooley apologized and referred to the incident as "a complete accident", claiming that he initially posted the photo without realizing it showed his genitals.

Cooley made several appearances in TV commercials for Easterns Automotive Group, a local car dealership group on the DC and Baltimore areas, alongside Clinton Portis, Antwaan Randle El, Sean Taylor and Jason Campbell.