Organised by Metropolis Comics via its auction arm ComicConnect.com, the transaction sets a new price record for the landmark issue, Bleeding Cool reports.
The 1963 issue was written by Stan Lee and illustrated by Jack Kirby. It featured the mutant team's original lineup of Angel, Iceman, Beast, Cyclops and Marvel Girl under the leadership of Professor X. Series antagonist Magneto also made his debut in the comic.
The recently sold copy bears a grading of 9.6 by the Comics Guaranty LLC. There are said to be two copies rated at 9.8 in existence, though it is not known how much they would raise in auction.
Earlier this year, ComicConnect.com sold a copy of Amazing Fantasy #15, which features the first appearance of Spider-Man, for $1.1 million (£670,000).
The record price paid for a comic is $1.5 million (£930,000) for the Golden Age Action Comics #1.