As a child, his family spent summers on Cape Cod up the road from The Harwich Junior Theater.

[2] Harrington has been featured as Dr. Simon O'Keefe on the WB drama Summerland, FBI Special Agent Paul Ryan on FOX's short-lived The Inside, and Steve on NBC's version of Coupling.

He had a recurring role in Season 4 of the TV Land comedy series Hot in Cleveland.

Harrington has appeared in films such as American Reunion (with his character again – like in Desperate Housewives – being called "Dr. Ron"), Whatever It Takes, Anywhere but Here, Catalina Trust, A Little Inside, and Partner(s).

He has also performed on stage, starring as Jack in Boy's Life and appearing in the off-Broadway productions Barefoot in the Park and Tony and Tina's Wedding, Harrington is an avid sports fan who plays in the Entertainment League, a private celebrity basketball league (formerly the NBA-E League), and skates for a local amateur ice hockey team.