Aiken was educated at private schools and at Harvard University, where he was a friend and contemporary of T.S. Eliot (Eliot, T.S.) (whose poetry was to influence his own). A tutor in English at Harvard in the late 1920s and a London correspondent for The New Yorker in the mid-1930s, he divided his life almost equally between England and the United States until 1947, when he settled in Massachusetts. Aiken was instrumental as editor of Selected Poems of Emily Dickinson (1924) in establishing that poet's posthumous reputation, and he played a significant role in introducing the work of American poets to the British public.

After three early collections of verse, Aiken wrote five “symphonies” between 1915 and 1920 in an effort to create poetry that would resemble music in its ability to express several levels of meaning simultaneously. Then came a period of narrative poems, several volumes of lyrics and meditations, and, after World War II, a return to musical form but with richer philosophical and psychological overtones. The best of his poetry is contained in Selected Poems (1929), which won the Pulitzer Prize for poetry in 1930, and Collected Poems (1953), including a long sequence “Preludes to Definition,” which some critics consider his masterwork, and the often anthologized “Morning Song of Senlin.” Aiken served as the poetry consultant to the Library of Congress (now poet laureate consultant in poetry) from 1950 to '52.

Most of Aiken's fiction was written in the 1920s and '30s. Generally more successful than his novels of this period were his short stories, notably "Strange Moonlight" from Bring! Bring! (1925) and "Silent Snow, Secret Snow" and "Mr. Arcularis" from Among the Lost People (1934). The Short Stories of Conrad Aiken was published in 1950, followed by A Reviewer's ABC: Collected Criticism from 1916 to the Present (1958) and The Collected Novels (1964). In spite of the many awards Aiken received, many critics have concluded that he never received appropriate recognition for his work.