His movie debut was in 2001's The Car Thief and the Hit Man. Donowho co-starred alongside Emile Hirsch in The Mudge Boy. In 2003 he was featured as the Drummer for a song in The Hermitt's "& The Story of The Insects". Donowho is known for his work in 2004's Imaginary Heroes with Emile Hirsch. In the film, Donowho plays a sexually ambiguous character.
Donowho's roles in Imaginary Heroes and later in A Home at the End of the World created for Donowho a positive relationship with the gay community. He appeared with brother Matthew at the 2004 Outfest, a gay and lesbian film festival held annually in Los Angeles along with the cast and crew of A Home at the End of the World. He appeared in Bringing Rain with Rodrigo Lopresti and Alexis Dziena. For the third season of The O.C., the producers cast Donowho as Johnny Harper. Donowho played Stanley in the 2006 film adaptation of Strangers With Candy but does not appear in the released version of the film.
