Justin Paul Theroux (/θəˈroʊ/; born August 10, 1971) is an American actor and filmmaker. He gained recognition for his work with director David Lynch in the mystery film Mulholland Drive (2001) and the horror film Inland Empire (2006). He also appeared in films such as Romy and Michele's High School Reunion (1997), American Psycho (2000), Charlie's Angels: Full Throttle (2003), Strangers with Candy (2005), Miami Vice (2006), Wanderlust (2012), The Girl on the Train (2016), The Spy Who Dumped Me (2018), On the Basis of Sex (2018), and Lady and the Tramp (2019).

Theroux was a screenwriter for films such as the action comedy Tropic Thunder (2008), the superhero film Iron Man 2 (2010), and the musical comedy drama Rock of Ages (2012). He made his directorial debut with the romantic comedy film Dedication (2007).

Theroux starred as Kevin Garvey in the HBO mystery drama series The Leftovers (2014–2017), for which he received widespread praise and was nominated for the Critics' Choice Television Award for Best Actor in a Drama Series. He also starred as Dr. James Mantleray in the Netflix comedy drama miniseries Maniac (2018). In 2021, he portrayed Allie Fox in the Apple TV adaptation of The Mosquito Coast, based on the novel by his uncle Paul Theroux.

Early life
Theroux was born on August 10, 1971, in Washington, D.C. His mother, Phyllis Grissim Theroux, is an essayist and author, and his father, Eugene Albert Theroux (born 1938), is a lawyer at Baker & McKenzie in Washington. Theroux is the nephew of the travel writer and novelist Paul Theroux, novelist and poet Alexander Theroux, author Peter Theroux, and novelist and educator Joseph Theroux; he is the cousin of British journalists and documentary filmmakers Louis and Marcel Theroux. His father is of half French-Canadian and half Italian descent. Through his mother, Theroux is a great-great-grandson of financier, banker and railroad magnate H. B. Hollins, and of music critic and author Gustav Kobbé.

Theroux took the name Jesus as his Catholic Confirmation name.

Theroux attended Lafayette Elementary School, Annunciation School, and the Field School. He first started acting while in high school at the Buxton School, in Williamstown, Massachusetts. He graduated from Bennington College in 1993 with a B.A. in visual arts and drama.