Early life and career
Theroux was born in Singapore,
the younger son of the American travel writer and novelist Paul Theroux, who was noted for "coming down hard" on Louis when he was younger for smoking cannabis cigarettes (or joints). His mother, Anne Castle, was Paul's first British wife. His elder brother is the writer and television presenter Marcel Theroux. He is the cousin of American actor Justin Theroux. He moved to the UK when he was 4, and was brought up in London. Theroux was educated for a couple of years at Allfarthing school then moved to Westminster School (where he was a friend and contemporary of the comedians Adam Buxton and Joe Cornish). Another of his contemporaries was Liberal Democrat politician, and Deputy Prime Minister of Great Britain, Nick Clegg with whom he travelled to America. He then went to Magdalen College, Oxford where he gained a first class degree in modern history and was noted for his film reviews for the Grapevine magazine.