The figure-hugging Jean Louis gown, with 2,500 crystals, was bought by the Ripley’s Believe It or Not museum chain, exceeding the USD 3 million guide price.
The company’s vice president said it was “most iconic piece of pop culture that there is”.
Monroe died from a drug overdose just three months after the performance.
The sultry rendition for President Kennedy’s 45th birthday at a 1962 Democratic fundraiser at New York’s Madison Square was one of her last public appearances.