He attended St. Pius X High School, in Houston, Texas, graduating in 2003. He was a member of their 1999 State Championship team. He was a two-time All-State selection and also earned All-district and First-team All-State honors as a senior when he recorded 50 tackles and seven sacks and was nominated for ESPN's Army All-American Game. He earned first-team All-State honors as a junior when he totaled 76 tackles and 13 sacks. He was honorable mention All-State honorable mention honors as a sophomore. He was a member of the high schoolhonor roll all four years.
College career
Harrington played college football for Texas A&M and started 36 of the 49 games he played in and recorded 156 tackles, 15 sacks and 25 stops behind the line of scrimmage. A two-time All-Big 12 selection, including First-team honors as a junior in 2006 when he played through a right shoulder rotator cuff tear and led the team in solo tackles, sacks and tackles for loss as a defensive end. In 2007, he played in 13 games while starting the last 12, totaling 58 tackles, two sacks, caused and recovered two fumbles and blocked a kick on his way to a Second-team All-Big 12 selection. In 2006, he played led the Aggies in solo tackles, sacks, and tackles behind the line of scrimmage while earning First-team All-Big 12 Conference. He also forced two fumbles and recovered one. In 2005 in his first year as a starter, he began the year by starting the first four games at left defensive end before switching to right defensive end for the remainder of the season. He totaled 25 tackles, four sacks and seven tackles behind the line of scrimmage. In 2004, he was the team's first reserve off the bench at defensive end and appeared in 12 games, posting 14 tackles, two sacks and five tackles for a loss. In 2003, he redshirted.
Professional career
Pre-draft
Harrington weighed and measured at 6-4⅜, 264 pounds at the 2008 NFL Scouting Combine. He did 21 reps of 225 pounds and ran a 4.84 40-yard dash. He broad jumped 9'9" and had a vertical leap of 37½".
Arizona Cardinals
Harrington was drafted by the Arizona Cardinals in the sixth round of the 2008 NFL Draft. He signed a three-year contract with the team shortly afterwards. Harrington played in all four of the Cardinals preseason games, producing 10 tackles and a sack, though was released during final cuts on August 30, 2008. The team re-signed him to the practice squad on September 24 after they released wide receiverOnrea Jones.
