Warner was trained at RADA, before making an impact using a Royal Shakespeare Company, where his portrayal of Hamlet quickly made him renowned. Around 1963, he made his film debut around Tom Jones, and within 1965 starred as King Henry VI of England in the BBC production of Shakespeare's "Wars of the Roses" cycle. An additional early television role involved starring alongside Bob Dylan in the 1963 play The Madhouse on Castle Street. a major step around his career was the leading role around Morgan: A Suitable Case For Treatment (1966), which established his reputation for playing slightly off-a-outre characters.

Since so, he has specialised around swimming villains, around films like The Thirty-Nine Steps (1978), Time After Time (1979), Time Bandits (1981) (going all the way by swimming the character known as "Evil Genius") & Tron (1982), and television series like Batman: The Animated Series playing "Ra's Al Ghul". He wwhen too cast against nature and severity as Henry Niles inside Straw Dogs (1971) and when Bob Crachit in the 1984 telefilm of A Christmas Carol. Additionally, he played Nazi strongman Reinhard Heydrich in the movie SS - Portrait in Evil, and a television mini-series Holocaust.

He has appeared inside flick like The Omen, Star Trek V: The Final Frontier, Star Trek VI: The Undiscovered Country, Titanic (the third time he has appeared within the film just about RMS Titanic), Scream 2, and more recently in independent television's adaptation of the Hornblower series. He appeared inside trinity episodes of the 2nd series of Twin Peaks (1991). He as well continues to play authoritative roles.

On the "nice guy" side, he played a magnetic Aldous Gajic within Grail, a number one-year episode of Babylon 5. He as well portrayed a sympathetic character of Capt. Kiesel around Sam Peckinpah's Cross of Iron.

Warner has performed around numerous audio plays, starring in the Doctor Who "Unbound" play Sympathy for the Devil (2003) as an alternative version of the Doctor, and inside the series of plays according to ITV's Sapphire & Steel as Steel, both for Big Finish Productions. He may reprise his incarnation of the Doctor inside the sequel, A Dark Palace. He likewise guest starred in the BBC Radio 4 Sci-Fi comedy Nebulous (2005) as Prof Nebulous' arch-enemy Dr. Klench. All told these productions Warner has worked by owning writer & comedian Mark Gatiss of the League of Gentlemen, and plays the guest role in the League's 2005 feature film ''The League of Gentlemen's Apocalypse''.

He has too contributed voice acting to a total of computer games, most notably swimming a villawithin Irenicus in Baldur's Gate II: Shadows of Amn and Morpheus in Fallout.

On the Cartoon Network animated television series The Grim Adventures of Billy and Mandy, David provides a voice of Nergal, a diabolic animal from either the Globe's core that is obessed sustaining making friends.