In March 1963, he went before the House of Commons to try to quell rumors about a sexual relationship. “There was no impropriety in my acquaintanceship with Miss Keeler,” he said.
But details kept coming out — British newspapers called it the “Scandal of the Century” — and he resigned in June 1963.
“I said that there had been no impropriety,” Mr. Profumo said in his letter of resignation. “To my very deep regret I have to admit that this was not true.”
Ms. Keeler had had multiple lovers, among them Cmdr. Eugene Ivanov, an attaché in the Soviet Embassy in London, and when that relationship came to light, government figures and MI5, the domestic intelligence agency, feared that her affair with Mr. Profumo might have created a grave security breach.
When Mr. Macmillan resigned later in 1963, the Profumo affair was often cited as a contributing factor.
Mr. Profumo died in 2006, having rarely spoken about the matter again. His wife, the movie actress Valerie Hobson, stood by him throughout, until her death in 1998 at 81.
Ms. Keeler, though, had a lot to say about the scandal over the years, including in “Secrets and Lies,” a memoir written with Douglas Thompson and published in 2012.
“I enjoyed sex and I indulged in it when I fancied the men,” she wrote, “but I was no hypocrite. It was others who were disguising their peccadilloes in dinner jackets, diamonds and evening dresses, indulging in weird fantasies.”
Christine Keeler was born on Feb. 22, 1942, outside London in Uxbridge. She left home at 16 and was dancing in a topless club in London when she met Stephen Ward, an osteopath who moved in fashionable circles.
“In reality,” she wrote in the book, “Stephen Ward was a spymaster who befriended hosts of prominent and powerful people in the British government, aristocracy and even members of the royal family.”
Newspapers said Mr. Ward ran a “vice ring.” He committed suicide in August 1963.
He introduced Ms. Keeler to Mr. Profumo in July 1961, at Cliveden House in Buckinghamshire. She had been swimming nude, “with Profumo watching approvingly,” Ms. Keeler’s book said.
Mr. Profumo, she wrote, seemed not to be a first-timer when it came to illicit affairs. (Headlines just last week in Britain told of his apparent relationship with a Nazi spy years earlier.)
“He knew the technique, what to say and when to brush his hand on your arm or accidentally touch your breast,” she wrote, calling him “a man with a wandering eye — and hands to match.”
Their dalliance did not come to light until months later, after another lover of Ms. Keeler’s, Johnny Edgecombe, apparently in a jealous fit, fired a gun outside Mr. Ward’s home, where she was staying. That incident led to court proceedings that brought out many of the details of the Profumo affair.
As part of the fallout from the events, Ms. Keeler served six months in prison for perjury and obstruction of justice stemming from false statements she had made about another lover, Aloysius Gordon.
“What I would like to do is to go into films,” she said upon her release in 1964. “I know I have got no experience as an actress and I don’t want to live on my notoriety, but I have got to begin somewhere.”
Though Ms. Keeler made some money by selling her story to the British newspapers, the film career never came about. But the Profumo affair made it to the big screen in 1989 in the movie “Scandal,” with Joanne Whalley playing Ms. Keeler and Ian McKellan as John Profumo.
“I’m sorry, but that film was just a snapshot of what really went on,” Ms. Keeler wrote. “The surface has barely been rippled.”
“Scandal” was hardly the first adaptation of the scandal. “The Christine Keeler Story” came out in late 1963, just months after the matter had made headlines. The BBC plans to begin shooting a six-part series, “The Trial of Christine Keeler,” next year.
Ms. Keeler was briefly married to James Levermore in the 1960s and to Anthony Platt in the 1970s. In addition to her son Seymour, her survivors include a granddaughter.
Ms. Keeler was sometimes described as a prostitute, a description she did not accept.
“It’s true that I have had sex for money,” she wrote in her book, “but only out of desperation, and that is still something that I hate to have to admit even to myself. Ironically, it has been sex for love or lust rather than for money that has always caused me more problems.”
Another woman who achieved some notoriety from the scandal was Mandy Rice-Davies, who shared lodgings with Ms. Keeler. In 2013, when Andrew Lloyd Webber mounted a short-lived musical about Mr. Ward, she recalled the promiscuity of the time.
“In those days, there were good girls and there were bad girls,” she told The Associated Press. “Good girls didn’t have any sex at all, and bad girls had a bit.”