It was printed on the first anniversary of the 1916 Easter Rising when rebels staged a major revolt against British rule in Ireland.
The Proclamation went under the hammer at Victor Mee Auctions in Co Cavan on Wednesday with an estimate of between €10,000 (£8,650) and €20,000 (£17,300).
Yesterday it was reported that the auction house had sold the item to a private client in Northern Ireland.
There are just three 1917 Proclamations known to still be in existence, and they were printed by republican women's group Cumann na mBan with the printing blocks used for the original version after they were gathered from the wreckage of the GPO.