It will be Olsen's first marriage and Sarkozy's second.
Their happy news emerges after the notoriously private couple were photographed wearing matching gold bands in the Hamptons, New York last month.
A representative for Mary Kate has yet to comment on the marriage.
She previously dated artist Nate Lowman for two years before their split in 2010. Charlotte filed for divorce in New York, and asked that the pre-nuptial agreement filed in France be set aside. In 2013 Mary-Kate and her sister took aim at their own critics by blasting people with a false perception of fame.
In 1997, Olivier married Charlotte Bernard, a freelance fashion writer and author of children's books who grew up in Paris They were officially married in Nantucket, but had a second wedding in France, performed by his half-brother, Nicolas as mayor of Neuilly-sur-Seine. Mary-Kate and Ashley insist the idea they have had everything handed to them is a ridiculous one, and they are proud to have gone back to college and worked for their careers in fashion.
Mary-Kate told Allure magazine: "I think people looked at us with the perception of 'Oh, you just have everything. "[Strangers assumed we] had enough money to just do nothing - or why would we go to college?
Set a date: Mary-Kate Olsen, 29, is set to tie the knot with Frenchman Olivier Sarkozy, 46, in The Hamptons in June 2016, according to a new report.
The couple are pictured at an event in East Hampton in August Sarkozy, 46, presented Olsen, 29, with a 4-carat vintage Cartier diamond ring after she accepted his second proposal last year, according to Us Weekly, and the couple live in a .5 million New York City apartment.
The former actress, who now works as a fashion designer tied the knot with French hunk Olivier - the half brother of former French President Nicolas Sarkozy in the last couple of days.
Sources close to the pair, who have been dating for nearly three years , say that they wanted a quiet ceremony with just a few family members.
Mary-Kate, 28, got engaged to dad-of-two Olivier, who at the age of 45 is 17 years her senior on Valentine's Day.
The pair live together in a mansion in the Hollywood Hills, Los Angeles.