He previously served as an assistant coach and the director of player development for the Brooklyn Nets of the National Basketball Association (NBA).

Harrington made an immediate impact, as a 13-year-old eighth grader, he hit four three-point baskets late in a game to lead his team to the Western Massachusetts Tournament Finals.

By the time his career was finished Harrington recorded a total of 2,347 points scored, which is still the highest in Western Massachusetts for boys.

Harrington left N.C. State after his freshman season and transferred to Auburn University playing for coach Cliff Ellis.

Harrington's final NBA game was played on April 16, 2003, in a 84 - 89 loss to the Houston Rockets where he recorded 9 points, 3 rebounds and 3 assists.

During the 2003–2004 season Harrington started in veteran's camp with the Washington Wizards before being released and signing in China for the Shaanxi Kylins.

He was there for a six-game stint before returning to the United States to play for the Columbus Riverdragons of the NBA Development League.

He also won the league's Inaugural 3-point Shooting Contest held in New Orleans as part of the D-League Dream Factory Friday Night skills competition.

For the 2009–2010 season, Harrington was signed to an NBA Development League contract and was allocated to the Springfield Armor based on territorial rights, to be part of their inaugural campaign.

On January 6, 2010, it was announced that Harrington had left the Springfield Armor and signed with Kotwica Kołobrzeg of the Dominet Bank Ekstraliga in Poland.

[3][4] On July 5, 2016, the Brooklyn Nets announced that Harrington was named assistant coach and director of player development.