Johansson's publicist, Marcel Pariseau, told The Associated Press the couple is engaged, after two years of dating. The representative said the couple has not set a date for their wedding yet.
This will be the 34-year-old Johansson's third marriage. She was previously married to actor Ryan Reynolds from 2008 to 2011, and French businessman Romain Dauriac from 2014 to 2017. She shares a daughter, 4-year-old Rose Dorothy Dauriac, with Dauriac.
As for Jost, 36, this will be his first marriage. He is best known as the co-anchor of Saturday Night Live's "Weekend Update," along with Michael Che, and is one of the show's top writers.
Johansson and Jost started dating in November 2017, appearing at the American Museum of National History gala in New York City that year. They managed to keep the relationship in the down-low until making their red carpet debut at the Avengers: Infinity War Los Angeles premiere last year. They also walked the red carpet for Avengers: Endgame together.
The engagement news came after sources told PEOPLE in March they were ready for marriage.
"Scarlett and Colin are in love and share many of the same interests and the same sense of humor," a source told the magazine. "Scarlett is very happy."
At the time, sources said Jost had not proposed yet, but said the relationship turned very serious very quickly.
"She is a mother and in a mature place where marriage makes more sense than it did in earlier relationships that didn't last," the source said. "She is in love and likes to be married, but is aware of how hard it is these days."
Johansson is best known around the world as Black Widow in the Marvel Cinematic Universe. The character made her debut in Iron-Man 2, and recently played the role in Endgame. She is also famous for keeping her private life out of the public eye.
It was only recently that Johansson opened up to USA Today about being her daughter.
"My daughter loves fairytale things. She loves girl things, princess stuff," Johansson said of Rose. "And I love it, too!"
She continued, "I love all the Disney princesses from back in the day. Now they're much more empowered than some of the older, classic ones."
"But you're sort of battling that a little bit, and you start to see how the dynamic of those classic fairy-tale stories affect the way that your children think about the male/female roles in society," she explained. "It's very black and white."
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