The ‘Under the Skin’ star, 28, who was previously married to Ryan Reynolds for two years before their divorce was finalised in June 2011, is set to tie the knot with the French journalist, who popped the question approximately one month ago.
A source close to the couple confirmed the news, saying: "They’re engaged and very happy." A spokesperson for the blonde beauty declined to comment on the news.
The couple began dating in November after being introduced by mutual friends, just weeks after the actress split from her boyfriend of one year Nate Taylor.
Earlier this week Scarlett was spotted wearing a diamond ring at the Venice International Film Festival in Italy. She was previously spotted wearing an ornate gold ruby ring in July but friends dismissed reports she was engaged at the time, saying it was "simply a piece of jewellery."
Rumours first began to swirl that the couple were planning to wed after the blonde beauty was spotted wearing a huge pear-cut diamond ring as she wandered around New York with Romain, 30, in February.
The ‘Avengers’ star admitted last year she liked being married but hinted that she wasn’t interested in tying the knot again for quite a while.
Scarlett said: "I got married when I was young and it was incredibly romantic and I liked being married, actually. "But it is different. It’s hard to put into words. To me, being in a functioning relationship doesn’t mean you have to be married.
"I never think about marriage. Is that weird? The only time I ever think about it is when people ask me. It’s really not important to me."