The 35-year-old actress complimented the low-cut, long-sleeved look with a pair of strappy, black Jimmy Choo heels.
Portman, who is expecting her second child with husband Benjamin Millepied, took home the Best Actress award on Sunday for her portrayal of Jacqueline Kennedy in the upcoming biopic Jackie.
Friend and fellow actress Susan Sarandon presented the award to the actress, and they both spoke with ET's Nischelle Turner backstage at the event, where they opened up about their fun night.
"I was looking forward to this evening because I got to spend time with Susan so I was very lucky," Portman shared.
Recently, Portman sat down with ET to talk about her turn as the former First Lady, and the expectant mom opened up about how her 5-year-old son, Aleph, and her forthcoming bundle of joy are her life's "good luck charms." Check out the video below to hear more.