Josiah has worked as an actor at theaters across the country, including Manhattan Theatre Club, Mark Taper Forum, Geffen Playhouse, American Repertory Theater, Shakespeare Theater of D.C., Rattlestick Theater, Portland Center Stage, and others.

He currently teaches scene study in the MFA program at Brooklyn College, specializing in the plays of Chekhov, Ibsen, and Shakespeare. He is also on faculty at HB Studio and Yale Summer Conservatory. Over the past decade, he has taught classes and workshops at Williams College Summer Conservatory, New York Conservatory for the Dramatic Arts, Western Oregon University, and Completely Ridiculous Conservatory—an online acting program that brought together student actors from across the US and Canada during the pandemic.

His approach to the work is highly dynamic. While his classes have their roots in Stanislavsky, he draws from a number of other systems and tools, including clown, physical games, elements of Michael Chekhov, and others, all in service of opening an actor's mind and body to their character from a place of curiosity and play.