Lessing has been nominated for the Booker Prize three times
Profile: Doris Lessing
The 87-year-old has been honoured with the 10m kronor (£763,000) award for her life's work over a 57-year career.
Her best-known works include The Golden Notebook, Memoirs of a Survivor and The Summer Before the Dark.
Lessing said she was "very glad" about the honour - particularly as she was told 40 years ago that the Nobel hierarchy did not like her.
She told BBC Radio 4: "I've won it. I'm very pleased and now we're going to have a lot of speeches and flowers and it will be very nice."
They can't give a Nobel to someone who's dead so I think they were probably thinking they had better give it to me now
Doris Lessing
"So now they've decided they're going to give it to me. So why? I mean, why do they like me any better now than they did then?"
The author, who turns 88 on 22 October, said she thought she had become more respectable with age.
"They can't give a Nobel to someone who's dead so I think they were probably thinking they had better give it to me now before I popped off," she said.
Lessing was told the news by reporters after returning from shops
And she is the second British writer to win in three years, after Harold Pinter was honoured in 2005. Turkish author Orhan Pamuk won last year.
The Swedish Academy, which awards the prize, described Lessing as "that epicist of the female experience, who with scepticism, fire and visionary power has subjected a divided civilisation to scrutiny".
"Oh good, did they say that about me?" she replied. "Oh goodness, well obviously they like me better now than they used to."
Lessing was out shopping when the announcement was made and said she thought a TV show was being filmed on her street when she returned to find TV crews outside her house.
Lessing was born in what is now Iran and moved to Rhodesia - now Zimbabwe - as a child before settling in England in 1949.
Her debut novel The Grass is Singing was published the following year and she made her breakthrough with The Golden Notebook in 1962.
'Pioneering work'
"The burgeoning feminist movement saw it as a pioneering work and it belongs to the handful of books that informed the 20th Century view of the male-female relationship," the Swedish Academy said.
But Lessing herself has distanced herself from the feminist movement.
The content of her other novels ranges from semi-autobiographical African experiences to social and political struggle, psychological thrillers and science fiction.
She has been nominated for the Booker Prize three times - for Briefing for a Descent into Hell in 1971, The Sirian Experiments in 1981 and The Good Terrorist in 1985 - but has never won.
In addition to the Nobel cash prize, Lessing will receive a gold medal and an invitation to give a lecture at the academy's headquarters in Stockholm. She can also expect to see a rise in sales.
US author Philip Roth had been the bookmakers' favourite for the award. His name has been mentioned in connection with the prize for many years, but he has always been overlooked.
Doris Lessing (2006). .
After lots of speculations and speculative London betting on the outcome it has been announced that British author Doris Lessing ("The Golden Notebook", 1962) is the winner of the 2007 Nobel Prize for Literature. 

At the International Book Fair at Frankfurt, Germany, which is currently underway, this decision has met with general approval, as a decision awarding the literary work of an author well established beyond her native country, rather than a political statement. The reason given for giving the prestigious award to Doris Lessing was to honour "that epicist of the female experience, who with skepticism, fire and visionary power has subjected a divided civilisation to scrutiny". 

Lessing herself, who will turn 88 on October 22, has been named a potential candidate over the last 30 years - so long in fact, that she herself once exclaimed: "I'll never get it". Finally, on December 10, 2007, the Nobel Prize including 10 million Swedish Kronor (€1.1 million) will be awarded to her in Stockholm, Sweden.