The much-publicised book sold 467,183 copies in its first week, according to official figures from Nielsen BookData.
The book, which was written with celebrity ghostwriter JR Moehringer, went on sale on 10 January.
Most of the revelations in the book leaked early after some copies went on sale in Spain several days before the official publication date.
But that does not appear to have damaged sales of Spare. The only books to have enjoyed higher first-week sales since Nielsen's records began were four Harry Potter novels and Dan Brown's The Lost Symbol.
The memoir sees Prince Harry describe his experience as a member of the Royal Family before he stepped back from official duties in 2020.
It provides behind-the-scenes details of the conflict he had with his brother, Prince William, the heir to the throne.
The book was released in a blaze of publicity, receiving widespread media coverage around the world.
The Wall Street Journal previously reported the book sold 1.4 million copies in its first day - including pre-orders - across the US, the UK and Canada.
It is the only non-fiction book in the all-time top 10 fastest-sellers since Nielsen started collecting data.