The pill dramatically changed women's lives, not least through saving many from early death or disease by providing protection against womb cancer.
And the longer the contraceptive is used, the greater the reduction in risk, a re-analysis of all available evidence by international researchers, including Australians, found.
Since 1965, an estimated 400,000 cases of endometrial cancer have been prevented by the pill's use in high-income countries, including about 200,000 in the past decade.
The findings, published in The Lancet Oncology journal, reveal that every five years of oral contraceptive use reduces the risk of the cancer by about a quarter.
In high-income countries, 10 years of use reduces the risk of developing the cancer before age 75 from 2.3 to 1.3 cases per 100 users.
The strong protective effect, which persists for decades after stopping the pill, means women who use it when they are in their 20s or even younger continue to benefit into their 50s and older, when cancer becomes more common, said study author Valerie Beral, from the University of Oxford.
"Previous research has shown that the pill also protects against ovarian cancer," Professor Beral said.
"People used to worry that the pill might cause cancer but, in the long term, the pill reduces the risk of getting cancer."
The researchers pooled data on 27,276 women with endometrial cancer in 36 studies from Australia, North America, Europe, Asia and South Africa.
Pills in the 1960s usually contained more than double the oestrogen of pills in the 1980s.
The study's results suggest the hormones in the lower-dose pills are still sufficient to reduce the incidence of endometrial cancer, the authors said.
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