St David's Church in Carmarthen closed in 2003 after storm damage.
The grade-II listed nineteenth century building - which still had its stained glass windows and pillars intact, sold for £1 to a developer.
Sean Roper, from Paul Fosh Auctions told Wales Online: "We have handled a number of churches for sale at auction over the years but this is certainly the biggest we have ever sold. It's a really impressive piece of property.
"We're selling the property on behalf of the developer who bought the church previously but who now says he has his hands full working on a number of his other projects including the renovation of a castle in north Wales."
Roper said the former church could be converted to flats, a town house or for community or commercial use, subject to planning permission.
It will be offered at Paul Fosh Auctions on 6th December at The Park Inn Hotel, Llanedyrn, Cardiff, starting at 5pm.
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