Arriving arm and arm together at Fig & Olive in Los Angeles, the Zero Dark Thirty Best Actress nominee and Gian Luca Passi de Preposulo sipped Perrier-Jouët Champagne in the main room before Chastain spotted her costar from last year's The Help, Viola Davis, and Davis's husband.
Chastain, 35, hugged and kissed the 31-year-old Passi, making it clear to all who saw them that the two are, in fact, a couple.
Further into the evening, which was sponsored by MAC Cosmetics and MaxMara, Chastain went over for a long chat with Daniel Radcliffe as her beau affably looked on.
On Katie, Chastain was asked if she had a boyfriend, and her reply was: "I do. But I will say I have a rule I don't date actors, so he's not in the business, at all. … He’s in the fashion industry."
Passi reportedly works as a manager for Moncler, which designs outerwear for men and women.
In all, the couple stayed for nearly an hour, and, besides Radcliffe, also talked at length with Silver Linings Playbook writer-director David O. Russell.
Reporting by REAGAN ALEXANDER
The 85th annual Academy Awards will air live on ABC starting at 7 p.m. ET/4 p.m. PT on Sunday, Feb. 24, from the Dolby Theatre in Hollywood.