Natalie Portman will compete for her second Oscar next month, a sign that one of America’s favorite ingénues has finally grown up.

Throughout her career, Portman has excelled at playing young even when she wasn’t. She made her film debut as a 12-year-old girl who snuggles up to an assassin in “Léon: The Professional.” In Zach Braff’s “Garden State,” she played a mentally unstable young woman who’s crazy about The Shins. In George Lucas’ second trilogy of “Star Wars” films, she played Princess Amidala, a living doll who does almost nothing but change outfits in each new scene.

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Portman’s first Oscar nod — for supporting actress — came for playing a young stripper in Mike Nichols’ “Closer” (2004). (She lost to Cate Blanchett in “The Aviator.”) Portman’s first win — for best actress — came for playing a fledgling ballerina on the verge of a nervous breakdown in “Black Swan” (2010).

Portman’s performance as Jacqueline Kennedy in the biopic “Jackie” seems like something different. The Israel-born, Syosset-raised actress not only bears a passing resemblance to the petite former first lady, she manages to capture Kennedy’s crowd-pleasing smile, lockjaw accent and fragile demeanor. It’s also a thoroughly adult role: a sheltered woman forced to grapple with death, loss and public service.

With “Jackie,” Portman, 35, is competing against such legends as Meryl Streep (“Florence Foster Jenkins”) and Isabelle Huppert (“Elle”). Win or lose, Portman can certainly say she held her own.