Winslet and Mendes, both Oscar winners, married in 2003 in the Caribbean and have one son together, Joe, 6.
The two have been secretly separated since the beginning of the year, according to their British law firm, Schillings, which circulated an e-mail announcing the surprise break-up to journalists Monday.
The couple's split is "entirely amicable and is by mutual agreement," according to the firm. Both Mendes and Winslet, who also has a child, 9-year-old Mia, from her first marriage to British director Jim Threapleton, remain "fully committed to the future joint parenting of their children," Schillings said.
Winslet, 34, and Mendes, 44, ruled the red carpet together during their seven-year marriage; Winslet took home a 2009 Oscar for her turn in "The Reader," while Mendes followed up on his 1999 Best Director win for "American Beauty" by helming flicks like "Revolutionary Road," which starred Winslet and Leonardo DiCaprio.
Winslet, who won a Golden Globe for her work in "Revolutionary Road," thanked Mendes during her acceptance speech for directing the flick and for encouraging her to push herself into her role.
"Thank you for directing this film, babe, and thank you for killing us every single day and really enjoying us actually being in such horrific pain," she said.
Winslet, nominated for six Academy Awards, shot to fame in James Cameron's monster hit, "Titanic," which also featured DiCaprio.
It remains unclear whether Mendes and Winslet have begun divorce proceedings.