The academy described Lessing as "that epicist of the female experience, who with scepticism, fire and visionary power has subjected a divided civilisation to scrutiny."
Few had tipped Lessing for the 10 million kronor prize. At 87, she is the oldest person ever to win, and only the eleventh woman since it was first awarded in 1901.
The author found out about the Academy's decision as she returned from a shopping trip to her home in West Hampstead, London.
"This has been going on for 30 years," said Lessing, who put down her shopping bag and sat on her doorstep, head in her hand, after reporters gave her the news.
"I've won all the prizes in Europe, every bloody one, so I'm delighted to win them all. It's a royal flush," she said, according to AFP.
Lessing is widely respected by her contemporaries as one of the most cerebral novelists of her generation. Author Margaret Drabble once described her as "one of the very few novelists who have refused to believe that the world is too complicated to understand.''
Lessing's name has long been linked with the Nobel Prize, but many believed the Swedish Academy would now never honour her. Asked in August why she had not won, Lessing told the Boston Globe that there was a "hidden" reason.
"At a big evening party in Sweden, back when my Swedish publisher was alive, a little grey chap from the Nobel Committee sat down beside me and said: "You'll never win the Nobel Prize. We don't like you," she said.
"It was so graceless. What was I to say? I didn't say anything. I've never found out why they don't like me."
Doris Lessing was born Doris May Taylor in 1919 to British parents in Persia (now Iran). The family moved to Southern Rhodesia in 1925, where they lived on a farm. She described her childhood in her 1994 autobiography, Under My Skin.
After leaving convent school at 14 she went on to work as a nanny, a telephonist, an office worker a stenographer and a journalist. She married twice - first to Frank Charles Wisdom, with whom she had a son and a daughter. They divorced in 1943 and in 1945 she married Gottfried Lessing, a German-Jewish immigrant.
Doris Lessing had a number of short stories published in Southern Rhodesia (now Zimbabwe), but it was only after her second divorce in 1949, and her subsequent move to London, that she started her writing career in earnest.
Race and empire are themes frequently explored by Lessing. In her debut novel, The Grass is Singing (1950), she examines the relationship between a white farmer's wife and her black servant.
Lessing's breakthrough came with The Golden Notebook (1962), a book that became a favourite for the feminist movement for its examination of the male-female sexual relationship from a woman's standpoint.
Lessing herself has said she does not want to be viewed as a feminist icon. She caused controversy in 2001 when she said she found herself "increasingly shocked at the unthinking and automatic rubbishing of men which is now so part of our culture that it is hardly even noticed."
"The most stupid, ill-educated and nasty woman can rubbish the nicest, kindest and most intelligent man and no-one protests."
In her latest novel, The Cleft, Lessing continues her exploration of the relationship between the sexes by constructing a mythical all female world into which men are suddenly introduced.
Under My Skin (1994) and Lessing's other autobiographical book Walking in the Shade (1997) are widely regarded as the high-point of her career. They were praised for capturing the last days of the British Empire.
Also notable is Shikasta (1979), which marked a venture into science fiction, something of which the Swedish Academy was rumoured to disapprove. This was blamed by some for Lessing missing out on the prize in the past.
A strident critic of apartheid in South Africa and racism in Southern Rhodesia, she was banned for many years from visiting either country. In Britain she became active in the Communist Party in the early 1950s. She later described joining the party as a "neurotic decision." and called communists "murderers with a clear conscience."
She remained active in support of numerous causes, however, and has been a committed campaigner against nuclear weapons.