[11][12] In 1998, Byrne appeared as a Jewish concentration camp survivor who is instrumental in the capture of a Nazi war criminal (played by Sir Ian McKellen) in the film Apt Pupil.
On television, he has appeared in Thriller, Tales of the Unexpected, The Professionals, The Devil's Crown, Smiley's People as Peter Guillam, Yes, Prime Minister, Lord Mountbatten: The Last Viceroy, Between The Lines, Sharpe, Hornblower, A Touch of Frost, (The episode "Quarry", in which he played the father of Allie Byrne, his real-life daughter), Agatha Raisin (Hell’s Bells), Midsomer Murders (The Ghost of Causton Abbey), The Mists of Avalon, Waking the Dead, The Body Farm, Honest, Hamish Macbeth, and Casualty.
From April 2008 to January 2010, Byrne starred in Coronation Street, as Ted Page, Gail Platt's long lost father and the ex-lover of Audrey Roberts.
[14][15] He also appeared in the 2010 film Harry Potter and the Deathly Hallows Part 1 as Gellert Grindelwald, a powerful wizard that had been defeated by Dumbledore and imprisoned at Azkaban.
[16] He played Alfred Maxwell in BBC's Casualty, a terminally ill man with motor neuron disease and his friendship with clinical lead Connie Beauchamp.