Slinger was born in Accrington, Lancashire. He trained at RADA, graduating in 1994. From there, he went to work at the Royal National Theatre and Shakespeare's Globe. He has also worked extensively with the Royal Shakespeare Company, including the Complete Works and This England: The Histories cycles, playing Richard II, Fluellen, Richard Duke of York and Richard III. He played Bernard Woolley, the Prime Minister's Principal Private Secretary, in the stage version of Yes, Prime Minister (Chichester/London, 2010). In 2011, he appeared again with the Royal Shakespeare Company in the title role of Macbeth, a new production by Michael Boyd which was the first Shakespeare play to appear in the revamped Royal Shakespeare Theatre. In 2012 he played Malvolio and Prospero for the RSC in London and Stratford, and in 2013 he played Hamlet. From May 2015, he started playing Willy Wonka in Charlie and the Chocolate Factory the Musical in London at Theatre Royal Drury Lane.
