Discovered on land at North Elmham, near Dereham, the circa 600 AD coin was created by French rulers of the time to increase their available currency.
Adrian Marsden, finds officer based at Norwich Castle Museum, said the object was probably buried with its owner.
The pendant was declared treasure by the Norfolk coroner on Wednesday.
Mr Marsden added: "This is an early copy of a Byzantine gold coin made in France.
"The Merovingians [French rulers] created copies of Byzantine coins from their bullion as there wasn't enough coinage coming in from the eastern Roman empire. How many of these copies were 'official' currency is hard to say."
The 23.5mm diameter pendant, created from an imitation of a gold solidus of emperor Maurice Tiberius (582-602 AD), features a suspension loop with three longitudinal ribs having been soldered to the edge of the coin immediately above the emperor's head.
"What's interesting is you have somebody in France copying a Byzantine coin which then also followed the trend of turning it into jewellery."
Mr Marsden said the coin was likely to have come to England as a result of export trade at the time.
"We see very few of these so it's an interesting find and one that we will hope to acquire for the Norwich Castle Museum collection."
Other items declared treasure at the coroner's inquest include an early-medieval Carolingian-style silver mount found in Barnham Broom, a hoard of 150 Roman coins discovered in Quidenham and an early-medieval biconical gold bead which would have been worn on high-status necklaces.

The drama, which stars Paul Dano, Lily James and James Norton, has also won rave reviews.
The adaptation of Leo Tolstoy's novel averaged 6.3 million viewers, peaking at 6.7 million.
It was up against ITV's Endeavour and spy drama Deutschland 83 on Channel 4, which averaged 4.4 million and 1.2 million viewers respectively.
War and Peace picked up 25% of the audience share, against 19% for Endeavour, 6% for Deutschland 83 and 4.1% for My Mediterranean with Adrian Chiles on BBC Two.
The costume drama has been written by Andrew Davies, who is best known for his 1995 adaptation of Pride and Prejudice starring Colin Firth.
'Sweeping victory'
In the Daily Telegraph Serena Davies gave it four stars, calling it "an excellent adaptation" and "smart storytelling on a truly epic scale".
Christopher Stevens in the Daily Mail called the opening hour-long episode "nothing less than a sweeping victory".
While The Guardian's Viv Groskop said: "It's hard to imagine how the BBC could have done a better job."
Downton Abbey star James plays Natasha Rostov in the drama, with Dano - who starred in 12 Years a Slave - as Pierre Bezukhov and Grantchester star James Norton as Prince Andrei.
The classic novel follows the three as they experience love and loss against the backdrop of Russia's wars with Napoleon.
It also stars Gillian Anderson, Rebecca Front and Stephen Rea, who were also praised for their performances.
The show has been made by the BBC in collaboration with The Weinstein company and will premiere on Lifetime, A&E and History channel in the US on 18 January.
An early-medieval gold pendant created from an imitation of a Byzantine coin that was found in a Norfolk field is a "rare find", a museum expert has said.
[NEXT_CONCEPT]
The first episode of the BBC's new costume drama War and Peace was watched by more than six million viewers.