His mother was a grammar school teacher and his father was a salesman for the American Leather Oak company.
He entered the Trappist Monastery at St. Joseph's Abbey in Spencer, Massachusetts in 1958, and then the Franciscan Seminary at Callicoon, New York in 1960.
Three Wogs, his first novel, was written during a stay in London and was briefly considered by the actor Roy Dotrice for performance by BBC television.
Critic Colin Marshall wrote “Defending of his prose, Theroux once likened it to 'a Victorian attic.'
He delivers more inner life than outer, more desire for vengeance than for anything else, and more sheer stuff per page—stuff you don't expect—than in any other novels.”[2] Steven Moore called him an "overlooked modern master".
Literary broadcaster Michael Silverblatt once questioned Theroux's "perverse appreciation" at how inaccessible his books are thought to be.“Perhaps he sees his finely-wrought works of language and their lack of purchase on the culture as an apocalyptic indictment of that culture, of the intellectually (and especially verbally) careless society that could corrupt them.
In 1995, The New York Times reported that one of its readers had noted the similarity of six passages in Theroux's 1994 survey of The Primary Colors with a 1954 book Song of the Sky by Guy Murchie.