The 35-year-old was accompanied by fashion executive Gian Luca Passi de Preposulo Friday at the Women in Film Pre-Oscar Cocktail Party in LA.
The couple arrived arm-in-arm and spent the evening sharing affectionate kisses, sipping champagne and chatting to Chastain's "The Help" co-star Viola Davis, reported Hollywood Life.
Chastain had said recently she was happy to be in a relationship with someone who isn't famous.
"I have a rule. No actors... I've only been on a couple of dates with one and I was so freaked out someone was going to take a picture of us, because they were famous. I realised I wanted just to be able to hang out with someone. And I didn't want to talk about the business.