Lewis appeared on Beverly Hills 90210 in 1997, playing a love interest of character Valerie (Tiffani-Amber Thiessen), and his most prominent role to date was in Sex and the City, where he was a fairly regular member of the show's cast in its final season as emerging young actor and waiter Smith Jerrod (aka 'Absolut Hunk'), the one man whose sincerity got to Samantha. He joined the WB's supernatural drama Charmed, where he played the recurring role of Dex Lawson, a love interest (and brief husband) of Phoebe Halliwell, who is played by Alyssa Milano.

Lewis has appeared in several films: My Bollywood Bride, a Hollywood/Bollywood romantic comedy where Jason plays the leading man opposite Bollywood actress Kashmira Shah (aka. Kashmera) and Mr. Brooks, a thriller, where he plays opposite Demi Moore and Kevin Costner.

On December 5, 2006, it was announced that Jason would be guest starring on upcoming episodes of Brothers & Sisters as a possible love interest to the Matthe