Warhol's Mao series was a response to US president Richard Nixon's visit to China in 1972.
He transformed the official portrait of the leader, in this case using the red and yellow colour scheme of the Cultural Revolution.
It was last sold at auction in June 2000 for £421,500.
The auction at Sotheby's in London also included the sale of Gerhard Richter's 1994 work Wand (Wall) for £17.4 million.
Lucian Freud's Head on a Green Sofa was also sold for £2.9 million.
The painting of society figure Belinda 'Bindy', Lady Lambton was created after Freud exchanged his fine, sable brushes for larger hogs' hair brushes and taught himself to work standing up. Freud believed it to be among his best works.