Jason McBain, a member of Derby Artefacts Recovery Club, was out exploring land on the outskirts of Belper when he unearthed the historical coin.
The coin, which is thought to date back as far as 40.A.D, is believed to be a Celtic Stater coin from the Iron Age.
Jason said: “I started digging through rubbish and then all of a sudden I got a good signal.
“So, I started to dig further and that was when I saw a bit of yellow sticking out of the ground.
“I pulled it out carefully and at first it looked like a button.
“That was until we realised that it had print on both sides.
“At that point the group leader said to me ‘Do you realise what you’ve found?’
“I’m told that there’s only been 55 found in the UK and most of those are in Lincolnshire.
“I’ve been doing digs on and off over the last few years and I’ve only recently got back into doing it.”
Jason, from Staveley, says he was the envy of his fellow club members when the significance of his discovery became apparent.
“There was certainly a few jealous people when I found it,” he added.
“It’s not often you find coins that are undamaged but this was just in a perfect condition.
“It was the find of a lifetime - you don’t find something like this every day.”
Alastair Willis is Finds Liaison Officer for the Derby and Nottingham area, based at Derby Museum and Art Gallery.
He is now in the process of verifying the find but says that it’s unique design sets it apart from other coins.
He said: “It’s quite an unusual coin as it’s dome-shaped and is not like most coins from that period.
“Early indications show it is based around the East Midlands, from a tribe called the Corieltauvi.
“We’re currently working on what denomination it is.”