Since graduating, he has worked for various TV companies in the U.S. and Britain while working on his novels. He has presented various documentaries about life in the former Soviet Union and has fronted arts programmes for BBC Four and More 4. In 2008 Marcel authored and presented The Great Russian Art Boom on Channel 4, exploring why Russian Billionaires were suddenly buying art. In March 2009 Marcel presented In Search of Wabi-Sabi for BBC Four, as part of the channel's Hidden Japan season of programming, which follows Marcel’s challenging, entertaining and moving journey through Japan as he tries to understand the Japanese people and their theory of aesthetics.
In March 2006 Theroux presented Death of a Nation on More 4. In which he explored Russia's post-Soviet problems including population decline, the growing AIDS epidemic and the persecution of the Meskhetian Turks.
Marcel is also a contributing editor to Travel and Leisure Magazine. A piece he wrote for them about travelling to the coldest town in the world was chosen to appear in “Best American Travel Writing 2000”, published by Houghton Mifflin.
The New York Times called his first novel, A Stranger in the Earth, “charming and sprightly... a buoyant novel that amuses and entertains.” His second novel, The Confessions of Mycroft Holmes: A paperchase, won the Somerset Maugham Award in 2002. Reviewing it in the New York Times, the critic John Lanchester described it as "exquisitely calculated...very satisfying." A Blow to the Heart is Marcel's third book, published in July 2006. His latest book Far North, published by Faber in March 2009, was shortlisted for the US National Book Award.