Coleby is the son of actor Robert Coleby and brother of actress Anja Coleby.He attended Somerset College on the Gold Coast, graduating in 1996.In the same year, he played the role of Colonel Juan PerĂ³n in the school's production of Evita.

Conrad is now a familiar face of Australia's stage and screen.

In 1999, before leaving drama school Coleby co-starred with, then little known, Irish actor Eoin Moloney in the TV movie "Sabrina Down Under", filmed in Australia's Hamilton Island.

Upon graduation Coleby then performed the role of Stuey alongside John Howard, Leanna Walsman and Brendan Cowell in the Sydney Theatre Company's Production of "The Recruit" directed by Robin Nevin.

He was then cast in episodes of Always Greener (2002) and Water Rats (2000) before landing the role of series regular Scott Zinenko on the Australian medical drama All Saints, which he played from 2001 to 2004.

Since late 2007 he has portrayed Roman Harris on the world wide soap opera Home and Away, but he played his last episode on 11 June 2009.

Conrad also performed the lead role of "Tom" in "The Glass Menagerie" written by Tennessee Williams for Queenslabd Theatre Company. Conrad has lately performed the part of the main cast of the popular Australian drama series, Sea Patrol, for the 2010 season of the show, playing the role of Dylan "Dutchy" Mulholland.

Conrad was nominated for a Logie in 2002 for "Best New Talent".

During the final years of All Saints Conrad also performed the role of Geoff alongside Steve Bisely, John Wood, Aaron Pederson and Jeremy Sims in the Sydney Theatre Company production of "The Club" by David Williamson at the Sydney Opera House.

Conrad also sung the principal role of "Lt Cable" in Roger and Hammerstein's "South Pacific" presented at the Theatre Royale in 2005.