"Jackie" is a searing and intimate portrait of the first lady in the week after John F Kennedy's assassination in 1963.
She is famous for jealously guarding her privacy, favoring a small wedding to a lavish celebrity ceremony and taking her grandmother's maiden name to shield her family from the limelight.
But Natalie Portman said Monday portraying grief-stricken Jacqueline Kennedy had taught her the virtue of celebrities giving more of themselves to the public.
"Jackie," Chilean filmmaker Pablo Larrain's first English-language feature, is a searing and intimate portrait of the first lady in the week after John F Kennedy's assassination in 1963.
Portman told journalists at the American Film Institute's AFI Fest in Los Angeles, where "Jackie" was getting its US premiere, how she admired the stoic and dignified face Jackie put on for the public.
"It's understanding that even when she was going through something incredibly private, it meant something to other people how she presented herself publicly," Portman, 35, said.
"It's like other people share in whatever you're going through and that's really impressive that she was able to do that," she added.
Born Neta-Lee Hershlag in Jerusalem to a doctor father and an artist mother, Portman has taken on tough roles since starting her big-screen career.
She got her break at age 11 in "The Professional," the tale of a hitman-for-hire (Jean Reno) who becomes the mentor to a young girl.
But she turned down 1996's "Romeo + Juliet" because of the age difference between her and Leonardo DiCaprio, and rejected the 1997 remake of "Lolita," which she deemed "sleazy."
She also signed on to "Anywhere But Here" (1999) with Susan Sarandon only after a nude scene was dropped.
"I value my private life and security way more than getting parts by flashing my boobs on some magazine or being a sex symbol in films," she said in a 2000 interview.
Portman won a best actress Oscar for 2010's psychological ballet thriller "Black Swan".
It was on the set of that film she met her future husband, French dancer and choreographer Benjamin Millepied, with whom she is expecting a second child.
She has been tipped for a second Oscar for her performance in "Jackie," with critics raving about how accurately she managed to capture Kennedy's voice and personality.
"The easier things were... the more superficial details like the way she talked and the way she moved and looked," Portman said on the red carpet at Hollywood's TCL Chinese Theatre.
"Those are things you spend a lot of time on but it's really the way she felt that takes the imagination and the real searching. The other stuff is like learning a skill as opposed to exploring your own depths."
"Jackie" peaks with the first lady's real-life strategy of painting a fairy-tale picture of JFK by using "Camelot" as a sobriquet for the Kennedy administration, an epitaph which stuck.
"I loved that she defined herself as a wife primarily, but then lived a life that was very counter to that where she was her own woman," said Portman.
"It was like she didn't know how to be any other way, except exactly herself -- very strong, very able to author her own story. And (she) really became the author of her own story and his story."
Fox Searchlight Pictures is scheduled to release "Jackie" in the United States on December 2.