Mathias was born in Swansea, south Wales. He is known for directing the film, Bent, and for directing highly acclaimed theatre productions in London, New York, Cape Town, Los Angeles and Sydney. He has also had a notable professional and personal partnership with the actor, Sir Ian McKellen, since the late 1970s. He was named one of the 101 most influential gay and lesbian people in Britain by the Independent on Sunday in 2006.
Mathias began his career as an actor, making his first appearance on screen in an episode of the cult BBC TV series, Survivors, in 1977 in a small role. In the same year, he played an Irish Guards lieutenant in the film, A Bridge Too Far.
His acting career continued into the 1980s, with minor appearances on TV and in films such as Priest of Love, which starred McKellen as D. H. Lawrence, and The Scarlet Pimpernel, starring Anthony Andrews, Jane Seymour and McKellen. Although he made one notable appearance in the film, White Mischief, in 1988 as Gerald Portman, his greatest achievements have come in directing and writing.
Another notable TV appearance by Sean, was on the show Minder (TV series) in 1982. The episode was entitled Broken Arrow, in which Sean played the part, of a young darts player, named Dafydd.
Mathias's play, Cowardice, was produced at the Ambassadors Theatre in London in 1983, starring McKellen, Janet Suzman and Nigel Davenport. Despite poor reviews, he was undeterred and followed it with Infidelities, which premiered at the Edinburgh Festival Fringe in 1985 before transferring to London's Donmar Warehouse. A Prayer For Wings, directed by Joan Plowright, was produced in Edinburgh in 1987 and, after winning a Fringe First awards, transferred to the Bush Theatre in London. Later plays include Poor Nanny in 1989, Swansea Boys in 1990.
His writing also includes a novel, Manhattan Mourning, published in 1988, and the BBC TV film, The Lost Language of Cranes, broadcast in 1992.
Mathias' career as a theatre director took off in 1988 with Exceptions. The following year, he directed a revival of Bent, the award-winning play by Martin Sherman that had opened on Broadway in 1979 starring McKellen. Performed as a benefit, this performance featured McKellen, Richard E Grant, Ian Charleson and Ralph Fiennes. After receiving critical acclaim, Mathias directed a full run in 1990 with McKellen alongside Paul Rhys and Christopher Eccleston, winning the City Limits Award for Revival of the Year.
Buoyed by this success, Mathias went on to direct hit shows in both London and on Broadway, including Pam Gems' adaptation of Chekhov's Uncle Vanya with McKellen and Antony Sher, Alan Bennett's Talking Heads (again with McKellen), and Noel and Gertie starring Patricia Hodge and Edward Petherbridge.
In 1994, Mathias won the London Critics Circle Theatre Award for Best Director for Noel Coward's Design for Living (with Rachel Weisz, Clive Owen, Paul Rhys and Rupert Graves) and Jean Cocteau's Les Parents Terribles, starring Sheila Gish, Frances de la Tour, Alan Howard and Jude Law. This transferred to the Ethel Barrymore Theatre on Broadway in 1995 as Indiscretions, with Law joined by Kathleen Turner, Eileen Atkins, Roger Rees and Cynthia Nixon. It earned nine Tony Award nominations including Best Director of a Play.
Mathias directed his first Stephen Sondheim musical, A Little Night Music, at the National Theatre in London in 1995, with Judi Dench and Siân Phillips. He had worked with Phillips before, directing her in another Pam Gems adaptation, Henrik Ibsen's Ghosts at the Sherman Theatre in Cardiff in 1993. He worked with her again in 1997, directing her as Marlene Dietrich in Marlene, which transferred to Broadway two years later and gained two Tony Award nominations.
Other London directorial credits include Antony and Cleopatra, starring Alan Rickman and Helen Mirren, in 1998, and Tennessee Williams' Suddenly Last Summer with Sheila Gish in 1999. His career moved across the Atlantic to New York, where, in 2001, he directed McKellen and Helen Mirren in August Strindberg's Dance of Death. He went on to direct this in London and Sydney in 2003. Also in 2001, he directed an off-Broadway production of Servicemen by Evan Smith. He followed this with a Broadway revival of The Elephant Man starring Billy Crudup the following year at the Royale Theatre.
In 2002, he returned to Sondheim to direct Company at the Kennedy Center Eisenhower Theater in Washington, D.C. as part of its Sondheim Celebration, with a cast including John Barrowman and Lynn Redgrave. Speaking to the Stephen Sondheim Society at the time, he said: "I always wanted to do Company; it's the first musical I ever fell in love with." As a youngster in South Wales, Mathias said, he used to listen to the original Broadway recording of the show and sing The Ladies Who Lunch with friends. "I couldn't believe the songs, the cynicism, the sexuality."
Mathias gave into the lure of panto, and for Christmas 2004 he directed Aladdin at the Old Vic in London, with McKellen as Widow Twankey alongside Maureen Lipman, Roger Allam and Joe McFadden. Due to its huge success, Mathias reunited with McKellen and Allam for a second run the following Christmas, with Frances Barber in the cast.
In 2005, Mathias directed Rebecca Lenkiewicz's Shoreditch Madonna at the Soho Theatre in London, starring Francesca Annis and Leigh Lawson. He returned to the US to direct Chekhov's The Cherry Orchard with Annette Bening, Alfred Molina and Lothaire Bluteau, which opened at the Mark Taper Forum in Los Angeles in 2006.
Mathias has been based in South Africa since 1997 after visiting the country with the National Theatre in 1994 for a series of workshops. He made his South African directing debut in 2004 with Jean Anouilh's Antigone, starring the South African actor John Kani. "I had fallen out of love with London," he told the Financial Times in October 2004. "I felt I had exhausted my life in London. I couldn't invent myself any more. My life was frenetic and there was never time to absorb experiences. Then I had a series of deaths of people close to me, my mother died and a long-term relationship broke up. After that, right then, I felt I had failed." In 2007, he directed novelist Edna O'Brien's only play, Triptych, in Johannesburg, starring leading South African actor Dorothy-Anne Gould.
He began 2008 by directing a revival of Ring Round the Moon, Christopher Fry's adaption of Jean Anouilh's comedy, L'Invitation au Château, starring Angela Thorne at London's Playhouse Theatre. He followed this with the UK production of Triptych at the Southwark Playhouse in London.
He directed McKellen and Patrick Stewart in Samuel Beckett's Waiting for Godot, which toured the UK in early 2009 before opening at the Theatre Royal Haymarket, London in May 2009. It was his first production as 2009 artistic director of the Theatre Royal Haymarket. His second play at the Theatre Royal Haymarket is due to be a stage version of Truman Capote's Breakfast at Tiffany's by Samuel Adamson, starring Anna Friel, opening in September 2009.
Despite his focus on theatre direction, Mathias is also known as a film director because of his first - and currently only - feature film, Bent, based on the play that propelled him to success. Released in 1997, it starred Clive Owen alongside a host of leading actors including McKellen, Mick Jagger, Rupert Graves, Jude Law and Lothaire Bluteau. It won the Prix de la Jeunesse at the Cannes film festival. Since 2004, Mathias has been planning to direct a new film set in South Africa, called The Colossus, which he has adapted from the novel, Manly Pursuits, by Ann Harries. Actors lined up for roles have included Rachel Weisz, Susan Sarandon, Colin Firth and Sir Ian McKellen.