She was born around Springs, Gauteng, an East Rand mining town outside Johannesburg, the daughter of Isidore and Nan Gordimer. Her parents were both Jewish immigrants, her father a watchmaker from Lithuania near the Latvian border, and her mother from London. Gordimer's early interest in racial and economic inequality in South Africa was shaped in part by her parents. Her father's experience as a Jewish refugee in czarist Russia helped form Gordimer's political identity, but he was neither an activist nor particularly sympathetic toward the experiences of black people under apartheid.Conversely, Gordimer saw activism by her mother, whose concern about the poverty and discrimination faced by black people in South Africa led her to found a crèche for black children. Gordimer also witnessed government repression firsthand, when as a teenager the police raided her family home, confiscating letters and diaries from a servant's room.

Gordimer was educated at a Catholic convent school, but was largely home-bound as a child because of her mother's "strange reasons of her own" (apparently, fears that Gordimer had a weak heart). Home-bound and often isolated, she began writing at an early age, and published her first stories in 1937 at the age of fifteen. Her first published work was a short story for children, "The Quest for Seen Gold," which appeared in the Children's Sunday Express in 1937; "Come Again Tomorrow," another children's story, appeared in Forum around the same time. At the age of 16, she had her first adult fiction published.

Gordimer studied for a year at the University of the Witwatersrand, where she mixed for the first time with fellow professionals across the color bar. She also became involved in the Sophiatown renaissance. She did not complete her degree, but moved to Johannesburg in 1948, where she has lived ever since. While taking classes in Johannesburg, Gordimer continued to write, publishing mostly in local South African magazines. She collected many of these early stories in Face to Face, published in 1949.

In 1951, the New Yorker accepted Gordimer's story "A Watcher of the Dead", beginning a long relationship, and bringing Gordimer's work to a much larger public. Gordimer, who has said she believes the short story is the literary form for our age, has continued to publish short stories in the New Yorker and other prominent literary journals. Gordimer's first publisher, Lulu Friedman, was the wife of the Parliamentarian Bernard Friedman and it was at their house that Gordimer met other anti-apartheid writers

Gordimer's first novel, The Lying Days, was published in 1953. In 1954, she married Reinhold Cassirer, a highly respected art dealer who established the South African Sotheby's and later ran his own gallery; their "wonderful marriage" lasted until his death from emphysema in 2001. It was her second marriage and his third. Their son, Hugo, was born in 1955, and is today a filmmaker in New York, with whom Gordimer has collaborated on at least two documentaries. Hugo Cassirer later married Sarah Buttrick, and had three children: Kate, Roland, and Conrad. Gordimer also has a daughter, Oriane (born 1950), by her first marriage.