The €17million EuroMillions jackpot ticket was sold at a Lidl store in Cavan.
The winner has yet to come forward and announcement was made as the National Lottery appealed for players to check their tickets.
The Quick Pick ticket was purchased at the Lidl Store at Creighan on the Athlone Road in Cavan on the day of the draw, Friday 12 December.
Emma Monaghan from the National Lottery said this was Ireland's second EuroMillions win this year, after a €250 million jackpot was won in Cork in June.
She urged the winner to sign the back of the ticket before making contact with the National Lottery's claims team.
Ms Monaghan also said they would always advise winners to seek legal and financial advice before coming to Lotto headquarters.
Two jackpot wins in Cavan have made two of the county's newest millionaires in the last two weeks, after a Lotto Daily Million prize was also won in Cavan on 30 November.
Eimear O'Sullivan, who is the Corporate Affairs Director of Lidl Ireland, said the company was "absolutely thrilled" to have sold the winning ticket, and that it was their biggest win to date.
She said the atmosphere in the store today was "electric" and it gave staff a "boost of excitement ahead of Christmas".
"The store team is absolutely thrilled to have played a small part in making one of our shoppers dreams come true and just before Christmas as well," she said.
Ms O'Sullivan said that the store team would be getting an "extra special bonus" and a Christmas party to celebrate the win.
