The announcement comes as the couple visits Italy while promoting Johansson's new film, "Under The Skin" at the 70th Annual Venice International Film Festival. The "Avengers" star was seen wearing a vintage art-deco engagement ring while walking down the red carpet alongside her new fiance.
News of the engagement comes as a surprise to many as the 28-year-old actress told Elle U.K. in February that she "never" thought about marriage and that it was "really not important for [her]."
Johansson has said her divorce from her first husband, Ryan Reynolds,"was devastating."
"It really throws you. You think that your life is going to be one way, and then, for various reasons or whatever, it doesn't work out."
There is no official date planned for the couple's wedding as of now.