“Nothing’s ever mine, not to keep,” the newly widowed Jacqueline Bouvier Kennedy mordantly observes midway through “Jackie,” Pablo Larraín’s relentlessly close-up take on history’s most iconized First Lady. She says it as she looks around the palatial House that tragedy is forcing her to swiftly vacate — and with Ladybird Johnson already perusing fabric samples, to boot — but she’s speaking of far more than just the roof over her head.

Eschewing standard biopic form at every turn, this brilliantly constructed, diamond-hard character study observes the exhausted, conflicted Jackie as she attempts to disentangle her own perspective, her own legacy, and, perhaps hardest of all, her own grief from a tragedy shared by millions. Provocative and entirely unsentimental in the speculative voice given to its subject’s most private thoughts on marriage, faith, and self-image, and galvanized by Natalie Portman’s complex, meticulously shaded work in the lead, “Jackie” may alienate viewers expecting a more conventionally sympathetic slab of filmed history. But in his first English-language project, Chilean director Larraín’s status as the most daring and prodigious political filmmaker of his generation remains undimmed.

Larraín is currently on a creative tear after his inventive literary study “Neruda” wowed Cannes mere months ago; any concerns that he might have gone soft on us by taking on an American prestige project are allayed before a word of dialogue is spoken in “Jackie.” Rather, it’s the first eerie, keening notes of the score by Mica Levi that put our fears to rest, even as everything else is set tinglingly on edge: No director who’d choose Levi, the young British experimental musician who gave “Under the Skin” its haunting siren’s wail, to aurally steer his film has any plans to play it safe. Coolly handsome as the film is, it’s a collation of aesthetic choices that push us persistently and ever-so-subtly into the discomfort zone. Sebastián Sepúlveda edits it into non-sequential shards of memory, jaggedly disarranged in the manner of post-traumatic consciousness, while cinematographer Stéphane Fontaine’s searching close-ups repeatedly step an inch too far into its subject’s already frail personal space.

But it’s Noah Oppenheim’s remarkable screenplay, not drawn from any credited sources, that takes the most startling liberties with Jackie’s fiercely guarded privacy. Even at her most emotionally riven, she’s portrayed here as a woman in canny control of her identity, switching between different masks for press, public, and associates, and wearing none only when truly alone.

A breathtaking sequence finds Jackie, finally unaccompanied in her wing of the White House, swirling through rooms, necking vodka, popping pills, and listening with rueful irony to Richard Burton’s Broadway recording of “Camelot.” Imagined or not by the filmmakers, it’s a version of Jackie Kennedy she’d never have counted on anyone ever seeing, not least given her painstaking personal dedication to preserving and displaying domestic evidence of the House’s previous inhabitants. “Objects and artifacts survive for far longer than people,” she tells the camera, a nervous smile plastered on her face, in her famous television special, “A Tour of the White House with Mrs. John F. Kennedy.” “They represent history, identity, and beauty.” “Jackie,” for its part, seeks to represent its subject beyond the cultivated objects and images we associate with her, from that bloodstained, bubblegum-pink suit downwards.

The filming of that televisual tour, nearly two years before the events of Nov. 22, 1963, is one frame by which “Jackie” hangs its cross-hatched impressions of her state of mind in the days following her husband’s death. The other is an arranged interview with Life journo Theodore H. White (credited in the film merely as “The Journalist,” and watchfully played by Billy Crudup), conducted a mere week after the event, during which a composed, tart-tongued Jackie taunts him with fragmentary reveals of her true self, while forcing him into complicity with her disguise. “Don’t think for one second I’m going to let you publish that,” she chides sharply, seconds after giving a teary, sense-led recollection of the shooting itself. Whether that fleeting, wrenching display of grief was a momentary lapse or a teasing, cynical put-on is one of many questions invited by Portman’s intricate performance — so layered in its sense of internal motivation and manipulation that the actress’s fine technical approximation of Kennedy’s froggy tone and phrasing seems the least of its achievements. (It may just trump her Oscar-winning turn in “Black Swan” as the most high-wire feat she’s ever pulled off.)

Between these two interview-led passages, Larraín and Oppenheim (stepping up hugely from previous writing credits on “Allegiant” and “The Maze Runner”) capture their protagonist in significantly less studied form: The immediate aftermath of the assassination throws up one wearying practical dilemma after the next as she attempts to find time and space to mourn. With her brother-in-law Bobby (Peter Sarsgaard, excellent) raging at their rudely curtailed political influence, Jackie regards the funeral arrangements as a critical opportunity to assert and cement JFK’s legacy — at a time when her advisors would like to keep the matter as low-key as possible.

Between sparring negotiations over the appropriate course of action, all too few officials pause to ask or even consider how she’s feeling. The film, on the other hand, invites us to listen in on her spontaneous confessions, whether to her friend and aide Nancy Tuckerman (a lovely, understated Greta Gerwig) or a candid Irish Catholic priest (John Hurt) — both in scenes that could derail these otherwise rigorous proceedings with conveniently cathartic sentiment, but wind up adding further emotional and intellectual nuances to the character. After opening up to the priest about the chillier patches of her marriage, he encourages her to take comfort in happier memories. “I can’t — they’re mixed up in all the others,” she replies.

“Jackie’s” intelligently disordered assemblage of facts and feelings is likewise difficult to parse. For away from its piquant, sometimes incendiary observations on celebrity, politics, and the present-tense construction of history, the film is also a stirring, deeply upsetting account of individual grief at any level of scrutiny. The complicated, colliding feelings of anger, confusion, and cold acceptance that come with any personal loss are mapped out here with a sense of fine-tuned chaos, with Levi’s astonishing score somehow playing them all: a lilting, hopeful flute note carried on an alien wash of strings, or a militaristic death march thrumming behind a graceful flutter of piano.

While he feels her pain, Larraín is also loath to leave his subject alone: The most intimate scenes of “Jackie” are often its most gasp-inducing, whether she’s washing blood out of her hair in the shower or telling her children why Daddy’s not coming home. Some viewers will take issue with the boundaries, or lack thereof, in this lucid portrait, but by deftly shuffling through her many reflections and self-reflections, Larraín crucially never lays claim to the “real” Jackie. “When something’s written down, does that make it true?” she asks White, placing the authenticity of his profile further in doubt, before smirking, “They have television now.” In this rich, challenging, endlessly teasing film, on the other hand, the screen provides just as many places to hide.