James J. Braddock, an Irish-American boxer hailing from New Jersey, once stood as a light heavyweight contender. However, after suffering a career-ending hand injury in the ring, he is compelled to abandon his boxing dreams. This turn of events brings mixed emotions to his wife, [Mae](lily-james); she is relieved to see him step away from the violent sport yet knows that their financial stability hinges on his ability to fight.
As the Great Depression unfolds, Braddock takes on grueling manual labor as a longshoreman to support their family, enduring the challenges of employment with his injured hand. Opportunities are scarce, and just when hope seems dim, a fortunate twist occurs. A last-minute cancellation from another fighter leads his longtime manager and friend, Joe Gould, to propose a one-night opportunity to earn much-needed cash. The bout is against the formidable Corn Griffin, the number-two contender in boxing.
In a stunning display of determination, Braddock shocks both boxing pundits and fans alike, achieving a remarkable third-round knockout of Griffin. This victory instills in him a renewed confidence; he believes that, despite the loss of function in his right hand, he has honed his skills with his left. Despite Mae's palpable objections to his return, Braddock cannot resist the call of the ring. Mae initially harbors resentment towards Gould, seeing his encouragement as a profit-driven scheme, until she learns that Gould’s own family is equally mired in hardship.
With each fight, Braddock inches closer to a possible shot at the heavyweight championship ruled by Max Baer. Driven by pride, he decides to reimburse the money he received from the government during his unemployment spells from his winnings. As his inspiring journey captures the public's imagination, the writer Damon Runyon coins the term "The Cinderella Man," symbolizing Braddock as a beacon of hope amidst the nationwide struggles.
After impressive victories over John Henry Lewis and Art Lasky, a title fight against Baer looms. Facing overwhelming odds as a 10-to-1 underdog, Braddock exhibits unwavering courage. Baer's reputation for destruction precedes him; the fight's promoter, James Johnston, insists that both Braddock and Gould watch footage of Baer’s past matches, to underscore the real danger that lies ahead, highlighting Baer’s history of fatal matches in the ring.
Unfazed by the intimidation tactics employed by the arrogant Baer, who even mocks Mae publicly, Braddock remains resolute. Mae, incensed by the blatant disrespect, retaliates by throwing a drink at him, yet she ultimately cannot bear to watch the fight at Madison Square Garden or even listen to the live broadcast.
On June 13, 1935, Braddock achieves what many deem one of the greatest upsets in boxing legend, defeating the seemingly unbeatable Baer to clinch the heavyweight championship title.
In a poignant epilogue, we learn that Braddock eventually loses his title to Joe Louis, who later reflects on Braddock's bravery, calling him "the most courageous man I ever fought." After his boxing career, Braddock finds stability by working on the construction of the Verrazzano Bridge, operating heavy machinery on the docks, and he and Mae finally purchase a house, where they will cherish their life together for years to come.
