He played Zach Stevens on the O.C.
Cassidy was born in Portland, Oregon. He attended La Salle High School in Milwaukie, Oregon and graduated from the Two-Year Conservatory program at The New Actors Workshop in New York City in 2003.
Cassidy is perhaps best known for his role as Zach Stevens throughout the second season of the television series The O.C.; his character had an on-again/off-again relationship with Summer Roberts. Cassidy also has a role in the movie Zoom.
In 2007, Cassidy played Cliff Wiatt in The CW television program, Hidden Palms.
Cassidy joined the cast of Smallville in the series' seventh season, starring as the new editor of the Daily Planet, Grant Gabriel, a love interest of Lois Lane. In truth, he was Julian Luthor, the cloned and aged brother of Lex. In the episode "Persona," Cassidy's character was shot dead, marking the end of his character's saga.
He played Charlie Hogan, Megan Smith's (Joanna Garcia) best friend in the first fifteen episodes of the CW show Privileged.[
He currently plays Tyler Mitchell on the TBS show Men at Work.