They went public with their romance six months later, making their red carpet debut as a couple at the American Museum of Natural History Gala in New York.
Scarlett and Colin have continued to support one another at events ever since, with the funnyman most recently joining his superstar girlfriend at the Los Angeles premiere of her latest Marvel blockbuster, "Avengers: Endgame", in April.
The actress' publicist, Marcel Pariseau, confirmed the engagement news to The Associated Press on Sunday, May 19, but details about Colin's proposal have yet to be revealed.
The marriage will be the 36-year-old's first, and Scarlett's third.
She was previously married to Ryan Reynolds for just over two years until December 2010, and she went on to secretly tie the knot with Romain Dauriac in October 2014, just weeks after welcoming their daughter Rose, now four.
She and Dauriac finalised their divorce in September 2017.