The Conspicuous Gallantry Medal awarded posthumously to Staff Sgt Jim Prescott, who was killed trying to defuse an Argentine bomb on HMS Antelope, went for £95,000 in the March 28-29 sale after being estimated at £80,000-100,000.
David Erskine-Hill of London auctioneers Dix Noonan Webb, who sold the medal group, said: "There have only been three Conspicuous Gallantry Medals issued during the present Queen's reign and this is the only one to an Army recipient, and a posthumous issue, so it is unique - and unique too for the Falklands War.
"Everything about it is absolutely a one-off, and I think it is important, too, as it is a closed history now the CGM is no longer awarded and, of course, the Falklands War is over.
"If it was still around and some were being awarded in Afghanistan then you wouldn't know what the final number might be, but this is finite, we know it, it's unique and that's it, end of story.
"It's an enormously difficult thing to put a price on and we are just happy it made its estimate, but above all clipped the top end of it."
Sgt Prescott was part of a two-man Royal Engineers bomb disposal team sent to HMS Antelope on May 23, 1982, but unknown to them the device had a 28-second delay and went off, killing him instantly and severely injuring his colleague, Warrant Officer John Phillips, who lost his left arm.
A photograph of the vessel sinking has become one of the most memorable images of the war.
Mr Erskine-Hill said that a collector bought the CGM, among a group of four awarded to Sgt Prescott.
CGMs were introduced by the Navy in 1855 as the naval equivalent to the Distinguished Conduct Medal and included the RAF in 1943 to recognise gallantry while flying in operations against the enemy. The Conspicuous Gallantry Cross replaced the CGM in 1993.
Dix Noonan Webb sold a CGM for just over £60,000 last December. It dated from the defence of the Legations in the Boxer Rebellion of 1901.
"We have sold quite a lot of Falklands material and more and more is appearing in the market," said Mr Erskine-Hill.
While a lot of this is down to demand during the 30th anniversary of the conflict, it "goes right across the board to, for example, the always popular awards to the Royal Marines and the Paras, and one or two examples we had not that long ago were to those who were in the original RM detachment who became prisoners when the Argentinians invaded".
The sale of Sgt Prescott's CGM came on the back of that December 2011 auction which included not only the Distinguished Service Cross awarded to his bomb disposal partner Warrant Officer Phillips but also the Distinguished Service Medal awarded to Chief Petty Officer Townsend of HMS Argonaut - aboard which ship both Prescott and Phillips had undertaken bomb disposal work the previous day to their medal-winning exploits on the Antelope.
Indeed, Townsend had won his DSM for working close to the unexploded bomb to which they were assigned.
Mr Erskine-Hill said: "Phillips's DSC - another unique award for Army bomb disposal work in the modern era - achieved a hammer price of £120,000, while Townsend's DSM raised £65,000, results that in the company of the £95,000 hammer price paid for Prescott's CGM add further weight to the recent surge of interest in post-War conflicts."