[2] After graduating from LAMDA in 2005, Ellis starred in British-Asian writer Shan Khan's play Prayer Room at Birmingham Repertory Theatre directed by Angus Jackson.
Charles Spencer in The Daily Telegraph wrote "William Ellis memorably nails the condescending certainty of charismatic Christianity".
[3] Ellis then went on to play Benvolio in the Nuffield Theatre production of Romeo and Juliet that toured Barbados as part of Holder's Season in 2006.
[12] Ellis began acting on screen in 2006 with small parts and in 2009 he portrayed Wiktor in The Courageous Heart of Irena Sendler.
In 2012 he took on the part of Compeyson in Mike Newell's Great Expectations and in 2015, he played The Earl of Chester in Queen of the Desert, directed by Werner Herzog.