Williams became interested in playwriting while at the University of Missouri (Columbia) and Washington University (St. Louis) and worked at it even during the Depression while employed in a St. Louis shoe factory. little theatre groups produced some of his work, encouraging him to study dramatic writing at the University of Iowa, where he earned a B.A. in 1938.

His first recognition came when American Blues (1939), a group of one-act plays, won a Group Theatre award. Williams, however, continued to work at jobs ranging from theatre usher to Hollywood scriptwriter until success came with The Glass Menagerie (1944). In it, Williams portrayed a declassed Southern family living in a tenement. The play is about the failure of a domineering mother, Amanda, living upon her delusions of a romantic past, and her cynical son, Tom, to secure a suitor for Tom's crippled and painfully shy sister, Laura, who lives in a fantasy world with a collection of glass animals.

Williams' next major play, A Streetcar Named Desire (1947), won a Pulitzer Prize. It is a study of the mental and moral ruin of Blanche Du Bois, another former Southern belle, whose genteel pretensions are no match for the harsh realities symbolized by her brutish brother-in-law, Stanley Kowalski.

In 1953, Camino Real, a complex work set in a mythical, microcosmic town whose inhabitants include Lord Byron and Don Quixote, was a commercial failure, but his Cat on a Hot Tin Roof (1955), which exposes the emotional lies governing relationships in the family of a wealthy Southern planter, was awarded a Pulitzer Prize and was successfully filmed, as was The Night of the Iguana (1961), the story of a defrocked minister turned sleazy tour guide, who finds God in a cheap Mexican hotel. Suddenly Last Summer (1958) deals with lobotomy, pederasty, and cannibalism, and in Sweet Bird of Youth (1959), the gigolo hero is castrated for having infected a Southern politician's daughter with venereal disease.

Williams was in ill health frequently during the 1960s, compounded by years of addiction to sleeping pills and liquor, problems that he struggled to overcome after a severe mental and physical breakdown in 1969. His later plays were unsuccessful, closing soon to poor reviews. They include Vieux Carré (1977), about down-and-outs in New Orleans; A Lovely Sunday for Crève Coeur (1978–79), about a fading belle in St. Louis during the Great Depression; and Clothes for a Summer Hotel (1980), centring on Zelda Fitzgerald, wife of novelist F. Scott Fitzgerald, and on the people they knew.

Williams also wrote two novels, The Roman Spring of Mrs. Stone (1950) and Moise and the World of Reason (1975), essays, poetry, film scripts, short stories, and an autobiography, Memoirs (1975). His works won four Drama Critics' awards and were widely translated and performed around the world.