Conleth Hill graduated from St MacNissi's College and later attended the Guildhall School of Music and Drama's acting program, graduating in 1988.
Hill made his Broadway debut in Marie Jones' Stones in His Pockets. For his work in the Canadian production of the play he received a Dora Mavor Moore Award. He played German professor Max Staefel in a 2002 television adaptation of Goodbye, Mr Chips (2002). He played "Mum" to Peter Kay's character "Geraldine McQueen" in Peter Kay's Britain's Got the Pop Factor... and Possibly a New Celebrity Jesus Christ Soapstar Superstar Strictly on Ice, a spoof on the talent show genre of programmes.
Since April 2011, he has appeared as Lord Varys in the television series Game of Thrones, based on the novel series A Song of Ice and Fire by George R. R. Martin. Martin hinted, in a February 2013 post on his website, that he thought Hill would be a good choice to play the title character in a TV show based on Martin's science fiction novel Tuf Voyaging. He appeared in the second episode of the second series of Peter Kay's Car Share as Elsie, the drunk deli counter supervisor.