Ngũgĩ was born in Kamiriithu, near Limuru in the Kiambu district of Kenya, of Gikuyu descent, and baptized James Ngugi. While attending mission school, he became a devout Christian. He received a B.A. in English from Makerere University College in Kampala, Uganda, in 1963; during his education, a play of his, The Black Hermit, was produced in Kampala in 1962. His family was caught up in the Mau Mau rebellion; he lost his stepbrother, and his mother was tortured.
He published his first novel, Weep Not, Child, in 1964, which he wrote while attending Leeds University in England. It was the first novel in English to be published by an East African. His second novel, The River Between (1965), had as its background the Mau Mau rebellion, and described an unhappy romance between Christians and non-Christians.
His novel A Grain of Wheat marked his embrace of Fanonist Marxism. He subsequently renounced English, Christianity, and the name James Ngugi as colonialist; he changed his name to Ngũgĩ wa Thiong'o, and began to write in his native Gikuyu. The uncensored political message of his 1997 play Ngaahika Ndeenda (I Will Marry When I Want) provoked President Daniel arap Moi to order his arrest. While in prison, he wrote another English novel, Petals of Blood (1978).
After his release, he was not reinstated to his job as professor at Nairobi University, and his family was harassed. He left Kenya in 1982 to live in self-imposed exile in London.
In 1980 he published the first modern novel in Gikuyu, Caitaani muthara-Ini (Devil on the Cross). He argued that African writers should use their native languages when writing, rather than European languages, to build an authentic African literature.
Subsequent works include Detained, his prison diary (1981); Decolonizing the Mind: The Politics of Language in African Literature (1986), an essay arguing for African writers' expression in their native language; and Matigari (1987), one of his most famous works, a satire based on a Gikuyu folktale.
In 1992 he became a professor of comparative literature and performance studies at New York University, and held the Erich Maria Remarque Chair.