Rescued from the Colorado River as an infant and raised by Shamus Tobin, tomboy Molly Brown is determined to find a wealthy man to marry. She journeys to Leadville, Colorado and is hired as a saloon singer by Christmas Morgan. After miner Johnny Brown renovates her cabin, the two wed, and he sells his claim in a silver mine for $300,000. Soon after the money Molly hid in the stove accidentally is burned, Johnny discovers the richest gold vein in state history.
The Browns and Shamus move into a Denver mansion, and Molly sets out to improve her social status by trying to ingratiate herself with the city's elite, all of whom snub her and her nouveau riche ways. She and Johnny go to Europe where they are embraced by royalty, and the couple return to Denver with their new friends. Molly's plan to introduce them to the people who formerly rejected her is derailed by Johnny's rough and tumble friends, whose unexpected and boisterous arrival ruins the gala party she is hosting.
Molly decides to return to Europe, leaving Johnny behind. She initially falls for the charms of Prince Louis de Lanire, but eventually decides she prefers to live with Johnny in Leadville. Setting sail for home aboard the Titanic, she becomes a heroine when the ship sinks and she helps rescue many of her fellow passengers. When her deed makes international headlines, Molly is welcomed home by Johnny and the people of Denver.