After graduating from Magdalen College, Oxford, Theroux moved to the United States and worked as a journalist for Metro Silicon Valley and Spy.

The New Yorker described Theroux's work as "a piercingly humane, slyly funny guide through the funkier passages of American culture".

There, he befriended comedians Adam Buxton and Joe Cornish,[14] and future Liberal Democrat leader and Deputy Prime Minister Nick Clegg, with whom he travelled to America.

[15] He also performed in a number of school theatre productions including Bugsy Malone as Looney Bergonzi, Ritual for Dolls as the Army Officer, and The Splendour Falls as the Minstrel.

[17] Theroux's first employment as a journalist was in the United States with Metro Silicon Valley,[18][19] an alternative free weekly newspaper in San Jose, California.

He also worked as a correspondent on Michael Moore's TV Nation series,[9] for which he provided segments on offbeat cultural subjects, including selling Avon to women in the Amazon Rainforest, the Jerusalem syndrome, and attempts by the Ku Klux Klan to rebrand itself as a civil rights group for white people.

[21] In Weird Weekends (1998–2000), Theroux followed marginal (mostly American) subcultures such as survivalists, black nationalists, white supremacists, and porn stars, often by living among or close to the people who were involved in them.

I'm not a matinee idol disguised as a nerd.In the series When Louis Met... (2000–02), Theroux accompanied a different British celebrity in each programme in their daily lives, interviewing them as they go.

[24] In an interview in 2015, Theroux expressed his intention to produce a follow-up documentary about Savile for the BBC to explore how the late entertainer had continued his abuse for so long, to meet people he knew closely, and examine his own reflections on his inability to dig more deeply into the first case.

Produced by Simon Chinn—a school friend of Theroux's—and directed by John Dower, the film covers Theroux attempting to gain access to the secretive Church of Scientology.

[28] Forbidden America is a three-part series focusing on social media use in the United States among several groups, including the alt-right, rappers and pornographic film actors.

[29] The first series started airing weekly on BBC Two on 25 October 2022 and features interviews from rapper Stormzy, actress Dame Judi Dench, musician YUNGBLUD, adventurer Bear Grylls, comedian Katherine Ryan and singer Rita Ora.

In the Weird Weekends episode "Infomercials", he featured as a live salesman for an at-home paper shredder for the Home Shopping Network.

[38] In December 2015, Theroux captained the team representing Magdalen College, Oxford on BBC Four's Christmas University Challenge.

It has led to more footage of Theroux's rapping ability being unearthed, leading the BBC to publish an article listing seven times he "proved he was a massive hip hop head".

[42] Theroux's first marriage was to Susanna Kleeman until they divorced in 2002;[43] he later told Sathnam Sanghera of the Financial Times, "What happened was that my girlfriend was living with me in New York.

[46] They lived in the Harlesden area of London[9][10] until temporarily moving to Los Angeles in early 2013, allowing him more time to focus on his LA Stories series.