Eggold was born in Lakewood, California, the son of Karen (née Benik) and James Frederick Eggold. Eggold graduated from Santa Margarita Catholic High School in 2002, where he participated in many school theater performances, and later from the University of Southern California's theater arts department in 2006. In 2006, Eggold made his professional television debut by way of a guest appearance on the show Related. He made his film debut the same year in the short film Con: The Corruption of Helm. Besides his success as an actor, Eggold writes music, plays guitar and piano, and sings in the band Eleanor Avenue.