Ngugi has achieved international recognition as East Africa's leading novelist. His stories address the struggles of Africans in Kenya during the colonial and post-colonial eras. Critics have focused primarily on the political impetus in Ngugi's novels, stories, plays, and essays. G. D. Killam asserts, "Ngugi felt from the outset of his career as a writer that writing should serve social and political purposes.’’ Ngugi himself, in an introduction to the story collection Secret Lives, states that his writing is "an attempt to understand myself and my situation in society and history.’’ Charles Cantalupe, calling Ngugi "East Africa's greatest novelist and essayist,’’ notes that Ngugi is ‘‘the most widely discussed and foremost African writer today in understanding the problems of postcolonial Africa." Cantalupe has also pointed out the international impact of Ngugi's work, despite the fact that it has been banned in his own country: ‘‘Since his exile from Kenya in 1982, the eloquence of Ngugi's novels, essays, and plays has rung out and echoed in nearly all the geographical and intellectual centers in the world of arts and letters, with the tragic exception of Kenya itself.’’ John Henrik Clarke refers to Ngugi as ‘‘a spokesman for African nationalism and for blacks and third world forces everywhere.’’

As described by Killam, the stories collected in Secret Lives "deal with the mature and moral worth of various aspects of original Gikuyu culture; of the effect of Christian teaching both in schools and the churches on the quality of African life; of the development of capitalism, class-consciousness, and human alienation as a new Kenya develops out of the independence struggle.’’ Killam notes that in these stories, Ngugi ‘‘exploits the similarities between Gikuyu and Christian legends. . .Drawing on legends from the past to make a comment on the present Ngugi offers implicitly a plea for a return to basic human values.’’ Secret Lives is divided into three sections: ‘‘Of Mothers and Children’’ (3 stories), ‘‘Fighters and Martyrs’’ (6 stories), and ‘‘Secret Lives’’ (4 stories). Killam explains that the stories in the second section, in which "The Martyr’’ appears, deal with ‘‘events in the period defined by the coming of the white man through his departure from Kenya,’’ and with ‘‘aspects of the contact between Christianity and Gikuyu religions.’’ In portraying these two cultures ‘‘in collision,’’ Ngugi demonstrates that ‘‘decent values, usually associated with original African values, suffer as a result of coming into contact with imported ones.’’ Killam asserts that ‘‘The Martyr’’ is ‘‘perhaps the best in the collection.’’ He explains, ‘‘The story is centred in the human losses the independence struggle provoked. There was death and suffering and ultimately everyone is made into a kind of martyr.’’ Kimani Njogu points to the element of storytelling itself in the political implications of the stories in Secret Lives: ‘‘At whatever vantage point these stories are told or received, they have throughout a combination of sharp social commentary with storytelling as a way for characters to represent their inner sufferings and anxieties. Apparently, storytelling is for Ngugi not an addition to the spirit of narrative, but an integral part of it.’’

Ngugi has received the highest critical acclaim for his novels. Killam notes that Ngugi's "purposes for writing are plain in the novels: each examines the consequences of public, political events as they affect the lives of individual members of the community.’’ Killam adds that Ngugi ‘‘can wed his public vision to his artistic capacity and produce novels which show how the lives of individuals are given impetus, shape, direction, and area of concern by the social, political and economic forces in the society.’’ His first published novel, Weep Not, Child (1964), takes place during the Mau Mau Rebellion against the European colonial presence in Kenya and centers on a Kikuyu family. A River Between (1965) is a love story about two people whose relationship is doomed by the cultural divide between traditional and Christian beliefs. In A Grain of Wheat (1967), the stories of four characters are told in a series of flashbacks during and after the fight for national independence for Kenya. Petals of Blood (1977) is set in the era after Kenya achieved national independence and offers a class-based critique of the conditions of peasants in Kenya due to capitalist exploitation at the hands of foreign investors and the upper classes within Kenya. Petals of Blood is Ngugi's most noteworthy, as well as his most political, novel to date. Devil on the Cross (1980) was written in both Kikuyu and English, and takes an allegorical form in which the Devil is a central character.

Ngugi's plays have received attention in part due to their political impact in Kenya. Critics generally agree that his best play, co-written with Micere Githae Mugo, is The Trial of Dedan Kimathi (1976). Ngugi was arrested and imprisoned for a year upon the production of the play Ngaahika Ndeenda (1977; I Will Marry When I Want), which criticizes the economic elite in Kenya.