The bones of what scientists believe to be "probably a new species" of the carnivorous allosaurus were discovered during a dig in Wyoming in the United States in 2013.
The 150-million-year-old skeleton, which is 70 percent intact, was snapped up by an unnamed French art collector, who promised that the specimen will be lent out to a museum.
He said it was the "only one of its species" to have yet been discovered.
Dinosaur expert Eric Geneste had earlier told AFP it was impossible to "classify the skeleton yet as a allosaurus" because it was more robust, "with longer shoulder blades and a different number of teeth".
"In fact there are as many differences between it and an allosaurus as between a human and a gorilla," he added.
The same French auction house sold an allosaurus called "Kan" for 1.1 million euros in 2016.
Mickeler said that "herbivores do not quite excite businessmen who buy dinosaurs the same way as carnivores do. They want to buy carnivores like themselves."
Part of the proceeds of the sale of the skeleton by a British collector will go to towards funding further archaeological digs.