The Croft Blend Fine Old Scotch was taken to France by Corporal William Mill in 1914 but was never opened and he brought it home with him when he returned to Dumfriesshire.
Cpl Mill served with the 3rd Volunteer Battalion of the King's Own Scottish Borderers and the bottle was stored in a suitcase under a bed at his home. It has since been passed down through his family.
Little is known about the blend of whisky but experts believe it was produced between 1892 and 1913.
Bidding will start at £2,000 for the bottle and the online auction will remain open for 10 days.
Visitors to the Scottish Whisky Auctions website will be able to see what the current price is before making an offer and the auctioneers are expecting "some interesting bidding" when it opens on Friday.
It is the oldest bottle ever sold on the site and auctioneer Peter Burns believes it remains in good condition despite its age.
A note written by Cpl Mill on the back of a photograph of him taken in 1908 is also part of the lot.
He said: "The bottle was produced between 1892 and 1913, as the glass bottle manufacturer, Cannington, Shaw & Co were using a particular stamp format during this period which is present on the base of the bottle.
"Apart from that, nothing is known about this bottle and the whisky inside it. It is truly a mystery and, despite casting the net far and wide for answers, through archivists, whisky writers, historical institutions and other knowledgeable individuals, not one single person has been able to shed any light on it.
"There is a very high likelihood that this is a one of kind and, when it appears on our website later this week, it could make for some interesting bidding activity."
Based in Glasgow, Scotch Whisky Auctions is the UK's biggest online auction site, with 10-day sales held each month.