The fossil, nicknamed "Apex," was said to be "among the most complete skeletons ever found," according to the auction house.
The estimated auction price was $4 million to $6 million, but the dinosaur's skeleton surpassed the valuation by a considerable margin.
It also broke the record for the auction price for a dinosaur fossil, of $31.8 million for the remains of a Tyrannosaurus rex nicknamed Stan, sold in 2020.
The buyer's identity, who beat six other bidders, was not revealed. The Associated Press, however, reported the buyer was a US national who intended to lend the skeleton to an institution for research in the United States.
Apex "has now taken its place in history, some 150 million years since it roamed the planet," said Cassandra Hatton, who heads Sotheby's science-related business.
She has called Apex "a coloring book dinosaur," for its well-preserved features.
What do we know about Apex?
Apex was discovered in May 2022 on the private land of paleontologist Jason Cooper in Colorado.
The remains of the stegosaurus are on display in different parts of the world, but Sotheby's said Apex is 30% larger than Sophie, the most complete stegosaurus on public display to date.
Standing at 3.3 meters (11 feet) tall and 8.2 meters long, the stegosaurus lived long enough to show signs of arthritis, Sotheby's said.
