After graduation, Hannah had parts in theatre productions, films and television, which included leading roles. He broke into the "big-time" with his appearance as Matthew in "Four Weddings and a Funeral" (1994). Since this breakthrough role, he has played a psychopathic killer alongside Helen Baxendale in "Truth or Dare" and a mystery-solving pathologist in "McCallum". He was a karaoke-mad dead-beat dad in "The James Gang", the alcoholic, pilfering but endearing, lovable comic-relief brother of the female lead in "The Mummy" (1999), "The Mummy Returns" (2001) and "" (2008) and a Monty Python-quoting romantic comedy love interest in "Sliding Doors" (1998). Hannah also starred in the axed U.S. series "MDs" (2002), as well as making guest appearances in "Alias" (2001), "Carnivàle" (2002) and "Frasier" (2003). In 2006 he starred in the drama series "New Street Law". In 2007–08, he played a starring role in the ITV crime drama "Cold Blood".