He previously had a small role in the BBC's animated Doctor Who webcast Scream of the Shalka.
Not originally cast in the production, Tennant was recording a radio play in a neighbouring studio, and when he discovered what was being recorded next door convinced the director to give him a small role.
He began filming the new series of Doctor Who in late July 2005.
Tennant's first professional role upon graduating from drama school was in a staging of The Resistible Rise of Arturo Ui costarring Ashley Jensen, one of a few plays in which he performed as part of the agitprop Theatre Company.
Tennant's first major TV role was as the manic depressive Campbell in the Scottish drama series Takin' Over the Asylum (1994).
Tennant has gone on record as saying that, contrary to tabloids reports, he was not upset at not being able to play the role in his own accent and in fact had never wanted to.
However he was pleased to be able to use his own accent in one episode, when the Doctor briefly masquerades as "Dr Jamie Mc Crimmon" of Edinburgh in Tooth and Claw – a nod to the Second Doctor's companion.
Tennant contributed to several audio dramatisations of Shakespeare for the Arkangel Shakespeare series (1998).