After a fierce bidding war, the letter was bought by the French Museum of Letters and Manuscripts in Paris.
The sale of the letter at the auction house Osenat in Fontainebleau, south of Paris, was more than five times the anticipated price.
Napoleon wrote the letter in 1816 when he was trying to learn English during his exile on the South Atlantic island of Saint Helena.
Napoleon was exiled to Saint Helena after his defeat at the Battle of Waterloo in 1815.
The one-page letter, dated March 9, 1816, is addressed to Napoleon's companion in exile Emmanuel, the Comte de las Cases, who had been teaching him English, the BBC reported.
In the letter Napoleon refers to a ship due to dock in St Helena within seven days, bringing news from Europe.
However, it is littered with errors, for instance it says: "He shall land above seven day a ship from Europe that we shall give account from anything who this shall have been even to day of first January thousand eight hundred sixteen."
Napoleon appears to have written the letter during a bout of insomnia, putting at the end: "Four o'clock in the morning."
The letter is one of just three in the world known to have been written in English by Bonaparte.
The former emperor died on St Helena in 1821 age 51.
The Comte de las Cases wrote a book about his time on the island, and recalled how Napoleon had wanted to learn the language of his British captors.