Born to Fante-speaking parents, with his father's side Armah descending from a royal family in the Ga tribe in the port city of Sekondi-Takoradi, Ghana, Armah, having attended the renowned Achimota School, left Ghana in 1959 to attend Groton School in Groton, MA. After graduating, he entered Harvard University, receiving a degree in sociology. Armah then moved to Algeria and worked as a translator for the magazine Révolution Africaine. In 1964, Armah returned to Ghana, where he was a scriptwriter for Ghana Television and later taught English at the Navrongo School.

Between 1967 and 1968, he was editor of Jeune Afrique magazine in Paris. From 1968-1970, Armah studied at Columbia University, obtaining his MFA in creative writing. In the 1970s, he worked as a teacher in East Africa, at the College of National Education, Chang'ombe, Tanzania, and at the National University of Lesotho. He lived in Dakar, Senegal, in the 1980s and taught at Amherst and the University of Wisconsin—Madison.

In Fragments (1971), the protagonist, Baako, is a "been-to", a man who has been to the United States and received his education there. Back in Ghana he is regarded with superstitious awe as a link to the Western life style. Baako's grandmother Naana, a blind-seer, stands in living contact with the ancestors. Under the strain of the unfulfilled expectations Baako finally breaks. As in his first novel, Armah contrasts the two worlds of materialism and moral values, corruption and dreams, two worlds of integrity and social pressure.

Why Are We So Blest? (1972) was set largely in an American University, and focused on a student, Modin Dofu, who has dropped out of Harvard. Disillusioned Modin is torn between independence and Western values. He meets a Portuguese black African named Solo, who has already suffered a mental breakdown, and a white American girl, Aimée Reitsch. Solo, the rejected writer, keeps a diary, which is the substance of the novel. Aimée's frigidity and devotion to the revolution leads finally to destruction, when Modin is killed in the desert by O.A.S. revolutionaries.

Not many African authors have dealt with the slave trade in the African past. However, this subject was touched on by Armah in Two Thousand Seasons (1973), an epic, in which a pluralized communal voice speaks through the history of Africa, its wet and dry seasons, from a period of one thousand years. Arab and European oppressors are portrayed as "predators," "destroyers," and "zombies". The novel is written in allegorical tone, and shifts from autobiographical and realistic details to philosophical pondering, prophesying a new age.

The Healers (1979) mixed fact and fiction about the fall of the celebrated Asante empire. The healers in question are traditional medicine practitioners who see fragmentation as the lethal disease of Africa.

Armah remained silent as a novelist for a long period until 1995 when he published Osiris Rising, depicting a radical educational reform group, which reinstates ancient Egypt at the center of its curriculum.

Armah has often been regarded as belonging to the next generation of African writers after Chinua Achebe and Wole Soyinka. At the same time he is said to "epitomize an era of intense despair." Especially Armah's later work have evoked strong reaction from many critics. Two Thousand Seasons has been labelled dull and verbose, although Wole Soyinka considered its vision secular and humane.

As an essayist Armah has dealt with the identity and predicament of Africa. His main concern is for the creation of a pan-African agency that will embrace all the diverse cultures and languages of the continent. Armah has called for the adoption of Kiswahili as the continental language.