Dimitriades was born in Sydney, New South Wales, Australia, the son of first generation Greek immigrants and is the youngest of three siblings, one brother called George and a sister Melissa. He grew up in Earlwood, a working-class suburb of Sydney. His parents divorced when he was twelve.
Dimitriades began his career in the 1993 Australian film The Heartbreak Kid and later starred in the spin-off TV series Heartbreak High, in which he played Nick Poulos. Dimitriades played an underworld figure, Warren Lanfranchi, in the 1995 Australian drama television series Blue Murder. In 2008, Dimitriades appeared in the TV drama Underbelly. His character's name was suppressed due to on-going legal precedings and a Victorian court injunction surrounding the real life person he portrayed in the TV series.
In 1998, Dimitriades played the protagonist Ari in the Ana Kokkinos film Head On. Dimitriades' performance in the role was critically acclaimed and earned him an AFI Award nomination. In 2001, he appeared in the Australian comedies Let's Get Skase and La Spagnola. He has had roles in the Hollywood films Ghost Ship and Deuce Bigalow: European Gigolo
Dimitriades has starred in several Australian TV series, including the police dramas Wildside and Young Lions. He has also had small guest roles in the Australian soap Neighbours and the science fiction series Farscape.
He has also appeared in many theatre productions including two plays by Louis Nowra for Griffin Theatre Company, The Woman with Dog's Eyes and The Emperor of Sydney.