The items belonged to Major Edward Francis Farrell, an officer with the Leinster Regiment.
The collection was recently rediscovered, having been stored away since the 1930s.
Described as "rare and exceptionally complete", it was bought at auction by a private Irish collector for 7,250 euros.
"Individual items often turn up, but it is very rare to get an entire collection," said auctioneer George Fonsie Mealy.
The lot includes Maj Farrell's uniforms, hats, leather boots and stirrups, his folding bed, roll-out mattress, folding chair and table, his fitted travel case, his cooker, cups and saucers, cutlery and other items.
Major Farrell was born in 1863 and was initially a member of the Royal Meath Regiment.
Based in Drogheda and Navan, Royal Meath merged with the Leinster Regiment at the outbreak of World War One.
Maj Farrell was appointed as Lt Col of the Fifth Battalion.
He suffered ill health on three occasions during active service, including pneumonia, and other respiratory problems and was allowed to come home.
He returned to County Meath and worked at Navan Barracks until his retirement.
Maj Farrell died on 14 January 1951.
"The fact that Maj Farrell came home due to ill health might explain why the collection is in such good condition," said Mr Fonsie Mealy.
"There is very little known about Maj Farrell, apart from the fact he fought in France for almost three years.
"The collection was packed away in the 1920s and 1930s in the bag which itself is part of the collection.
"It is really quite rare to find a complete collection in such good condition," he added.
A spokesperson for the Imperial War Museum in London said:  "Having all these items together is very rare and they provide an interesting snapshot of what an officer would have had with him in France during World War One."
The auction took place in Castlecomer, County Kilkenny.
The complete collection of the personal belongings of an Irishman serving in the British army during World War One has been sold at auction.