Gethin attended Ashton Hayes Primary School, Ashton Hayes, Cheshire and Christ Church Primary School, New Malden, Surrey. He attended the Tiffin School in Kingston-Upon-Thames. He received a Scholarship to the British American Drama Academy in London from July to August 2004. Anthony studied English Literature at Oxford University's Balliol College and was President of the Oxford University Dramatic Society, before training at London Academy of Music and Dramatic Art.
He played Grigory in Boris Godunov at the Royal Shakespeare Company in Stratford-upon-Avon from November 2012 to March 2013.
He has appeared in Ten Days to War and Doctors, and played william in Copenhagen. His most notable roles are Renly Baratheon in the HBO series Game of Thrones and Charles Manson in NBC's Aquarius. In 2017, he voiced the character of Gil Brodie in the video game Mass Effect: Andromeda.
