The sunfish (mola mola) was discovered on the sand at Holme-next-the-Sea by a local walker.
The fish – the second largest bony fish in the world – is found around the globe but in UK waters is more common off the south west coast.
Sunfish can reach 1,000kg – the weight of a small car – and more than three metres in length.
Those that reach the UK tend to be much smaller, but they are still round and remarkably narrow.
It is listed as vulnerable on the International Union for Conservation of Nature’s (IUCN) Red List, because it is often a bycatch of the fishing industry.
Emma Cockburn, who found the fish, said: “It looks like it may have been hit by a boat. It’s come a heck of a long way.”
READ MORE More aquatic animals farmed than fished in 2022 in world first – UN | Eastern Daily Press
Ms Cockburn also found a dead porpoise on the beach.
Both discoveries were reported to the Norfolk Wildlife Trust.