In a 2005 radio interview with Amy Goodman of Democracy Now!, Thelwell said: "I didn't really become black until I set foot in this country (America).
"[3] Thelwell is widely known for his 1980 novel The Harder They Come, based on the film of the same title about the life and death of real-life Jamaican folk-hero Ivanhoe "Rhyging" Martin.
The novel was praised by Nigerian novelist Chinua Achebe (who bestowed on Thelwell the Igbo name Ekwueme, meaning "the man who always does what he says he will")[4] and by literary critic Harold Bloom, who included it in his appendix to The Western Canon.
Thelwell has also written two screenplays (Washington Incident, 1972; Girl Beneath the Lion, 1978, with Paul Carter Harrison).
Literary awards Thelwell has received include fellowships from the Rockefeller Foundation, the Society for the Humanities, the National Endowment for the Arts and the Centennial Medal of the Institute of Jamaica.