Sean got interested in acting after performing in a play at summer camp one year. He attended Byram Hills High School in Armonk, New York, at the same time as actors Eddie Cahill and Eyal Podell. In 1997 Sean graduated from New York University with a Bachelor of Arts in drama, and has studied theatre with the Tisch School of the Arts in London, The Collaborative Arts Project Twenty-One, Shakespeare Scenework, the Experimental Theater Wing, and the Playwright's Horizons Theater School, which he stayed with longest and has described as "home away from home". His theatre credits include regional productions of "Doors", "Yerma", "Berlin, Berlin", "Over the Tavern, Part II", "Book of the Night", "Severity's Mistress", and "Into the Woods".

In 1999, Sean got his first big break when he was cast as the lead in the Fox television series "Ryan Caulfield: Year One". Even though the series was cancelled after only two episodes had aired, Sean's performance was noted favourably by critics. He was shortly afterwards cast in the recurring role of Adam Matthews, a love interest for Neve Campbell's Julia Salinger, during the last season of "Party of Five". Sean then played an ex Navy SEAL turned Wall Street trader in "The $treet" - another show that was cancelled. In 2001, Sean was cast as football player Brian Piccolo in the ABC/Disney remake of "Brian’s Song".

In 2002, Sean became part of Joss Whedon's series "Firefly", playing refugee Dr. Simon Tam. The series was cancelled after only 11 of 13 episodes were aired, but quickly became a cult hit and found success in its DVD release.

Sean made his feature film debut in 2004 starring in the independent film, "Living ‘Til the End", and in 2005 reprised the role of Dr. Simon Tam in Joss Whedon’s film, "Serenity". In December 2006 Sean was back on TV screens in A&E's Movie of the Week "Wedding Wars" playing Ted Moore, boyfriend of lead character Shel, a gay wedding planner played by John Stamos.

Sean took some time off from acting after this, but started reading scripts again in autum 2007.

According to his bio, Sean is single and splits his time between living in New York and Los Angeles.our local post office.