The Oscar-winning actress wed Ned Rocknroll, Richard Branson's nephew, in front of her two children and a small number of friends. She was given away by Leonardo DiCaprio, her co-star in the films Titanic and Revolutionary Road.
According to reports, their marriage plans had been kept a closely guarded secret following their engagement in the summer.
The actress is reported to have met her new husband while she was at Branson's holiday home on Necker Island in the Caribbean last year. The house burned down after it was hit by lightning and Winslet was reported to have led her two children and Branson's mother to safety.
Winslet, 37, separated from her second husband – American Beauty and Skyfall director Sam Mendes, with whom she has a son, Joe – in 2010, after nearly seven years of marriage.
With her first husband, assistant director Jim Threapleton, she had one daughter, Mia, before they divorced after three years of marriage, in December 2001.
Rocknroll, 34, who changed his name from Abel Smith, works at Virgin Galactic, Branson's space travel venture, as head of marketing, promotion and astronaut experience. Until last year he was married to Eliza Pearson, the 24-year-old daughter of Viscount Cowdray. They married in 2009.
The Sun reported that Winslet and Rocknroll's wedding took place in a converted barn and was attended by just six friends from each side.
Winslet's spokesman said: "I can confirm that Kate Winslet married Ned Rocknroll in New York earlier this month in a private ceremony attended by her two children and a very few friends and family.
"The couple had been engaged since the summer."
One unnamed source told the Sun: "They are both so happy and very much in love. Kate is very private and didn't want anyone to know."
The actress achieved worldwide fame for her role in the 1997 blockbuster Titanic, starring opposite DiCaprio.
She won a best actress Oscar for the postwar romantic drama The Reader and accepted a CBE earlier this year for services to drama.
At the time – 100 years after the "unsinkable" Titanic went down – she spoke of her love of acting but said being a mother was the "best job".
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