Tennant's first professional role upon graduating from drama school was in a staging of The Resistible Rise of Arturo Ui co-starring Ashley Jensen, one of several plays in which he performed as part of agitprop 7:84 Theatre Company.

Moving to London in the early 1990s, Tennant lodged with comic actress and writer Arabella Weir, with whom he became close friends and then godfather to one of her children. He has subsequently appeared alongside Weir in many productions; as a guest in her spoof television series, Posh Nosh; in the Doctor Who audio drama Exile and as panellists on the West Wing Ultimate Quiz on More4.

Tennant developed his career in the British theatre, frequently performing with the Royal Shakespeare Company for whom he specialised in comic roles such as Touchstone in As You Like It, Antipholus of Syracuse in The Comedy of Errors and Captain Jack Absolute in The Rivals, although he also played the tragic role of Romeo in Romeo and Juliet.

Tennant appeared in several high-profile dramas for the BBC, including Takin' Over the Asylum (1994), He Knew He Was Right (2004), Blackpool (2004), Casanova (2005) and The Quatermass Experiment (2005). In film, he has appeared in Stephen Fry's Bright Young Things, and as Barty Crouch Jr. in Harry Potter and the Goblet of Fire. One of his earliest big screen roles was in Jude (1996), in which he shared a scene with his Doctor Who predecessor Christopher Eccleston, playing a drunken undergraduate who challenges Eccleston's Jude to prove his intellect.

Tennant's name was put forward as a possible candidate for the role of the Ninth Doctor for the new series that began in March 2005, although the role eventually went to Christopher Eccleston. With Eccleston's announcement on 30 March that he would not be returning for a second series, the BBC confirmed Tennant as his replacement in a press release on 16 April. He made his first, brief appearance in the episode The Parting of the Ways (2005) after the regeneration scene, and also appeared in a special 7-minute mini-episode shown as part of the 2005 Children in Need appeal, broadcast on 18 November 2005.

He began filming the new series of Doctor Who in late July 2005. His first full-length outing as the Doctor was a sixty-minute special, The Christmas Invasion, first broadcast on Christmas Day 2005. He was also seen in early December in the ITV drama Secret Smile.

Tennant has expressed enthusiasm about fulfilling his childhood dream. He remarked to an interviewer for GWR FM, "Who wouldn't want to be the Doctor? I've even got my own TARDIS!"

Tennant had previously had a small role in the BBC's animated Doctor Who webcast Scream of the Shalka. Not originally cast in the production, Tennant happened to be recording a radio play in a neighbouring studio, and when he discovered what was being recorded next door managed to convince the director to give him a small role. This personal enthusiasm for the series had also been expressed by his participation in several audio plays based on the Doctor Who television series which had been produced by Big Finish Productions, although he did not play the Doctor in any of these productions. In 2004 Tennant played a lead role in the Big Finish audio play series Dalek Empire III. He played the part of Galanar, a young man who is given an assignment to discover the secrets of the Daleks. In 2005, he starred in for Big Finish, recreating his role of Brimmicombe-Wood from Doctor Who: Unbound – Sympathy for the Devil. The play was recorded between Tennant getting the role of the Doctor and it being announced. He also played the title role in Big Finish's adaptation of Bryan Talbot's The Adventures of Luther Arkwright (2005).

Tennant has confirmed that he will continue to play the Tenth Doctor at least into the revived programme's third series in 2007,• and the Sun has reported that he has also signed for the fourth (2008) series, "in a £1 million deal".• The Daily Mirror has reported that Tennant is forbidden from attending Doctor Who fan conventions while he is playing the role.•

Tennant's casting in Doctor Who has not prevented him from taking on other roles. In January 2006, Tennant took a one-day break from shooting Doctor Who to play Richard Hoggart in a dramatisation of the 1960 Lady Chatterley's Lover obscenity trial, The Chatterley Affair. Written by Andrew Davies and directed by Doctor Whos James Hawes for digital television channel BBC Four, Hoggart's son Simon Hoggart praised Tennant's performance in The Guardian newspaper. "Extremely convincing — the suit, the hair, the Yorkshire accent, and trickiest of all, the speech rhythms. The only thing wrong is his sideburns. To do this film he had to take 24 hours off from making Doctor Who in Cardiff and, as he explained, the sideburns wouldn't grow back in a day."•

On 17 March 2006, the Daily Mirror reported that Tennant would star in an upcoming adaptation of H. G. Wells' comic novel The History of Mr Polly for ITV. There has, however, been no official confirmation of this. On 18 April 2006, The Guardian announced that Tennant would star in Recovery, a 90-minute BBC1 drama written by Tony Marchant. Tennant will play Alan, a self-made building site manager who attempts to rebuild his life after suffering a debilitating brain injury in a car accident.•