In the first term he was spotted by Philip Prowse and was invited to perform in Oscar Wilde's A Woman of No Importance at the Glasgow Citizens Theatre, playing the illegitimate son, Gerald.
Running parallel to Rhys's film work has been a diverse and notable television career, working in leading roles with directors such as Mike Hodges, Stephen Frears, Sir Richard Eyre, Philip Martin, Christopher Morahan, Tom Vaughan, Edward Hall, Harry Bradbeer in productions including Tumbledown, A Dance to the Music of Time, The Heroes, Ghosts, Gallowglass, The Healer, Anna Karenina, The Deal, Beethoven, The Ten Commandments, Borgia, Luther and Spooks.
In 2014, he played the lead as traitor Aldrich Ames, in The Assets miniseries, then as King George III in Turn: Washington's Spies and as Sir John Conroy in Victoria.
He appeared as Edmund in Long Day's Journey into Night and as Leo in Design for Living at The Donmar Warehouse, performing opposite Rachel Weisz and Clive Owen.
[7][8] In 2016, he starred in a new version of Chekhov's Uncle Vanya by Robert Icke at The Almeida Theatre alongside Tobias Menzies, Jessica Brown-Findlay and Vanessa Kirby.
Real-life characters played by Rhys have included Vlad Tepes, Ludwig van Beethoven,[9] Peter Mandelson,[10] Paul McCartney, Thomas De Quincey, A. E. Housman, Frédéric Chopin, Marcus Tullius Cicero and Charles Talleyrand.
[11] In the title role in Howard Brenton's play Paul at the Royal National Theatre, he was unable to continue as he had lost an unhealthy amount of weight, dropping from 76 to 57 kilograms (168 to 126 lb).