In 1993, Tiernan appeared in the series Cracker in the episode "To Say I Love You". In 1997 played Banquo in the Shakespeare adaptation for BBC (MacBeth on the Estate) alongside James Frain and Susan Vidler. In 1998, in the British TV series Hornblower, he played Bunting in the second episode, "The Examination For Lieutenant". Other credits in television include Victor Carroon in The Quatermass Experiment, Kim Trent in Life on Mars and Lenny Spearfish in the BBC TV series Jonathan Creek (2004) "The Curious Tale of Mr Spearfish". In 2005, he played Ben Jonson in A Waste of Shame, a william Shakespeare biopic presented as part of the BBC's ShakespeaRe-Told series. He appeared in an episode of crime drama Midsomer Murders as Steve Bright, a photography enthusiast who is strangled with his own camera strap and in Dalziel & Pascoe as a lottery winner in the two-part episodes "Fallen Angel". In 2012, he appeared as DS Hunter in BBC's new drama Prisoners' Wives.