In 1931, at the age of 16, Thomas left school to become a junior reporter at the South Wales Daily Post. His position with the Post didn't last long, though, as he quit in December 1932 and turned his attention away from journalism and back to poetry, now a full-time pursuit. Remarkably, about two-thirds of Thomas' oeuvre is from his late teens.
Thomas soon found success. His poem "And Death Shall Have No Dominion" was published in 1933 in the New English Weekly, marking his first international publication. The event sent Thomas to England in the summer of 1933 to meet with editors of various English literary magazines. He moved to London shortly thereafter and stayed for 10 years.

Thomas began doing reading tours to bring in income, and his readings were more like flamboyant performances than staid poetic events. He toured the United States four times, with his last appearance taking place at the City College of New York in October 1953. A few days later, after a long drinking bout at Manhattan's White Horse Tavern, Thomas collapsed at the Chelsea Hotel. He died in a New York City hospital not long after, on November 9, 1953, at the age of 39. Three causes of death were given during Thomas's postmortem examination: pneumonia, swelling of the brain and a fatty liver.

Thomas' poetry remains famous because of its originality. Aside from being a Welsh poet who wrote entirely in English, his work was (and still is) hard for critics to categorize. He refused any association with other literary groups, and his poetry never seemed to involve current or socially popular themes.