Charlize Theron, 39, and Sean Penn, 54, got engaged in November 2014 while they were on a trip to Paris, a source told Us Weekly.
According to the source, Theron and Penn "decided to take their relationship to the next level" and while there was no engagement ring given by Penn to Theron, the two are committed.
Theron and Penn came out together as a couple in public in December 2013. In an interview with Vogue in June 2014, Theron said she wants a long-term relationship and is not afraid of it.
"I never had the dream of the white dress. And watching other people getting married? I think it's beautiful for them, but to be quite honest, usually I'm sitting there just devastated," Theron told the magazine. "It's supposed to be this night of celebrating love, and all you see is a couple separated all night making sure everybody else is okay."
In addition, Theron explained that getting married "looks like a lot of work, and as you get older, you start sifting through the stuff that really matters."
While Theron, who has one two-year-old adopted son named Jackson, has never been married, Penn has been married twice before. He was married to "Material Girl" hit maker Madonna from 1984 to 1989 and to Golden Globe winner Robin Wright from 1996 to 2010.
Meanwhile, Madonna is reportedly trying to win Penn back by texting ad calling him nonstop. Claiming Penn as the "love of her life," she is said to be determined to win her former husband back.
"Madonna told me she has everything she wants, but she needs a soul mate. She says Sean is her soul mate," a source told National Enquirer.
The source added that Madonna sees Penn now as a mature person who is able to handle a mature relationship.