He became more critical of America, which he accused of war-mongering especially in Vietnam. At the End of the Open Road (1963) won him the Pulitzer Prize. In Adventures of the Letter I (1971), Simpson wrote poems about Russia and his Russian ancestors and about the most ordinary forms of American life. In Collected Poems (New York, 1988), he includes all the poems that he wants to preserve from his earlier books. Besides poetry, he has also written one novel, an autobiography, and autobiographical essay, and several works of other poets.
A well-known scholar and critic, Simpson has published a number of literary studies, including Three on the Tower: The Lives and Works of Ezra Pound, T.S. Eliot, and William Carlos Williams (1975), The Character of the Poet (1986), and Ships Going Into the Blue: Essays and Notes on Poetry (1994). Simpson also wrote a novel, Riverside Drive (1962), and the autobiographies North of Jamaica (1972) and The King My Father's Wreck (1994).
Simpson’s later work includes The Owner of the House: New Collected Poems (2003), a collection that spans his sixty-year career, and Struggling Times (2009). In addition to the Pulitzer Prize, Simpson has received numerous awards and accolades, including the Prix de Rome, the Columbia Medal for Excellence, and fellowships from the Guggenheim Foundation. He has been a finalist for the prestigious Griffin International Poetry Award, and his translation of Modern Poets of France: A Bilingual Anthology (1997) won the Harold Morton Landon Translation Award. Simpson lives in New York State.