The seven-metre long skeleton was discovered in the United States in 2014 and was only expected to fetch up to €1.5 million.
The world’s largest triceratops skeleton has sold for €6.6 million at a Paris auction house.
The sale to a private American collector on Thursday is a European record for a dinosaur fossil.
The enormous skeleton -- known as "Big John" -- is estimated to be over 66 million years old and was only found in 2014 in South Dakota in the United States.
It was named after the owner of the land where it was found and is certified by the Guinness World Records as the largest documented skeleton of a triceratops.
The three-horned dinosaur died in an ancient flood plain on the island continent stretching from present-day Alaska to Mexico, allowing the conservation of its skeleton in mud.
Researchers at the Italian universities of Bologna and Chieti carried out restoration work on the find to enable researchers to study the fossil.
The hammer price at the Hôtel Drouot auction house, before commission and other costs, was €5.5 million. It was only estimated to fetch between €1.2 and €1.5 million.
"It’s a record for Europe," auctioneer Alexandre Giquello said.
The triceratops skeleton of "Big John" measures 7.15 meters long and stands 2.7 meters high at the hips. The skull represents more than one-third of its total length, with two large horns over one metre long.
The skeleton is unique in that it is more than 60% complete and its skull more than 75% complete.
"The overall quality of Big John really deserved this price," said Iacopo Briano, a palaeontology expert, "for a triceratops and for a herbivore, this is an unbelievable record."
Djuan Rivers, a representative for the anonymous buyer of "Big John", said the collector was "absolutely thrilled with the idea of being able to bring a piece like this to his personal use".
"The history behind this and the duration of it is absolutely impressive," Rivers added.
"To be able to be a part of preserving something of this nature ... it’s also something extremely special."
Last year, a Tyrannosaurus rex skeleton reached over €27 million in an auction in New York, becoming the most expensive dinosaur ever sold.