The urn was discovered in Ballyshannon in County Donegal and is believed to be around 4,000 years old. It contained human remains that are yet to be identified. Suspected to be from the Bronze Age, the urn has now been removed for further examination.
Archaeologists say it is among a number of discoveries made on the Donegal site.
Tamlyn McHugh of Fadó Archaeology, the site’s excavation director, told BBC Radio Foyle of her excitement over the find.
She said: “It’s really nice to find, it seems to be in pretty good condition and it’s actually upturned, so it’s an inverted urn.”
The nature of the discovery prompted the on-site team to call in a more specialised and expert conservator.
According to Ms McHugh, there is evidence in Ballyshannon of three different types of Bronze Age burial.
She said it was an era that saw practices move towards singular burials.
“We’ve got the pit burials – the cremated remains and charcoal in very shallow pits – at least 12 of these, what we call a flat cemetery,” she said.
“Then we have the ring ditch, the urn was in that, and then we have the boulder burial.
“It is really interesting that we have all three together”.
Archaeologists will now use radio-carbon dating on the artefact.
This will allow them to “see a sequence, and see what came first, what came last, and get an idea of which burial practices came before the other,” Ms McHugh added.
The archaeological work is part of the €21m (£18m) construction of the new Sheil Community Hospital in the Donegal town.
The Health Service Executive (HSE) said the cremated remains recovered from the site will now be analysed by an osteoarchaeologist.
Shane Campbell of the HSE welcomed the groundbreaking discovery.
He said: “The HSE would like to thank Tamlyn McHugh and Fadó Archaeology for their painstaking work in uncovering these significant historical artefacts and ensuring they are properly conserved.”