Dozens of Christie associates were in the room clutching their phones as they took orders from potential buyers.
Prior to the sale, the portrait was estimated to go for about $200 million, according to Christie's.
In a statement, Christie's described the 40-inch (100-centimetre) by 40-inch portrait as "one of the rarest and most transcendent images in existence."
Warhol began creating silkscreens of Monroe following the actress's death from a drug overdose aged just 36 in August 1962.