The simplest of stories can reveal the most complex human truths, a verity that comes to taut, emotionally affecting life in “Two Days, One Night.” Written and directed by brothers Jean-Pierre and Luc Dardenne, this deceptively straightforward film — set in a working-class community in the filmmakers’ native Belgium — hews to the most streamlined contours of classic drama, with a protagonist racing the clock while encountering a series of obstacles, each of which affects the ultimate journey in tiny but life-changing ways. It’s a reflection of the particular genius of the Dardennes and the mesmerizing personal power of leading lady Marion Cotillard that “Two Days, One Night” winds up possessing such inexorable power, building to a climax that counts as one of the most hard-won and triumphant of the season.

Cotillard plays Sandra, an employee in a company that makes solar panels, who has just returned to work after taking medical leave. In her absence, management discovered that her job could be handled by other workers. In what seems like a stroke of purposeful cruelty, her bosses have left it to Sandra’s colleagues to decide if they want to keep her on or receive their usual annual bonuses. Sandra discovers the scheme just two days before the vote, meaning she has just that long to persuade her co-workers to cast their ballots her way.

The Dardennes are best known for their austere, naturalistic portraits of the marginalized and dispossessed; they usually work with relatively unknown actors, certainly none as glamorous or famous as Cotillard. This departure serves them spectacularly well: Virtually devoid of makeup, her hair pulled back in a finger-combed ponytail, Cotillard portrays Sandra through superb physical expressiveness, her face and body conveying both resignation and stubborn self-belief as she dutifully seeks out her peers to lobby them one by one. (Since they’ve already staged a preliminary vote, in some cases she’s trying to convince them to change their original ballot.)

Following Sandra as if she’s the main player in a present-day documentary, the Dardennes stay at an intimate but discreet distance as she works up the courage to knock on doors and interrupt weekend rituals. Each encounter conveys its own tough truth about what a globalized economy looks and feels like at the most local level.

Meanwhile, Sandra is supported by her superhumanly patient husband, played in a sympathetic turn by Fabrizio Rongione.

Although “Two Days, One Night” is clearly on Sandra’s side, the filmmakers ensure that everyone has his or her say as to why they decide to vote the way they do. As time ticks by, the Dardennes keep the tension as taut as a thriller; viewers may be surprised to discover just how much they care about Sandra’s ultimate fate, despite her own foibles and fatalistic tendencies.

As a parable on karma, capitalism and Darwinian corporate politics, “Two Days, One Night” can often feel brutal. As a testament to connection, service, sacrifice and self-worth, it’s a soaring, heart-rending hymn.

★ ★ ★ ★

PG-13. At Landmark’s Bethesda Row.
Contains some mature thematic elements.
In French with subtitles. 95 minutes.