He came to prominence in Four Weddings and a Funeral (1994), for which he was nominated for the BAFTA Award for Best Actor in a Supporting Role as Matthew.

John Rebus in Rebus (2000–2001); Jack Roper in New Street Law (2006–2007); Jake Osbourne in Cold Blood (2007–2008), Quintus Lentulus Batiatus in Spartacus (2010–2011), Jack Cloth in A Touch of Cloth (2012–2014), Jason's father (Aeson) in the BBC series Atlantis (2013–2015), Dr Holden Radcliffe in Agents of S.H.I.E.L.D.

At the suggestion of a colleague, after completing his apprenticeship he then attended the prestigious Royal Scottish Academy of Music and Drama.

He played a psychopathic killer alongside Helen Baxendale in Truth or Dare, and a mystery-solving pathologist in McCallum.

However, Rebus was later taken in-house by STV Productions, and Hannah was replaced in the leading role in the series by Ken Stott.

[citation needed] Hannah played the Monty Python-quoting love interest of Gwyneth Paltrow in the romantic comedy Sliding Doors (1998).

In many of his interviews, he mentions stories from their relationship, such as their visit to London's Sri Siam restaurant where he proposed to her in writing on the tablecloth.