Hundreds of thousands of unionists signed the Ulster Solemn League and Covenant in 1912 as they pledged to resist Home Rule on the island of Ireland.
The plate was used to print copies of the covenant during the turbulent constitutional crisis.
It is one of a series of historically significant lots related to the political upheaval on the island in the early decades of the 20th century which went under the hammer at Bloomfield Auctions on Tuesday.
An Irish flag that once flew from republican leader Michael Collins’ state car sold for £2,800.
In recent months, the auction house sold a stick once used by Mr Collins for £52,000 and a lock of the IRA commander’s hair for £18,000.
Karl Bennett, Bloomfield Auctions’ managing director, described a huge amount of interest in the covenant printing plate.
“This year marks 110 years since the signing of the Ulster Covenant and 101 years since the formation of Northern Ireland and I think that makes the sale of the printing plate much more poignant,” he said.
“I was very pleased to see it make £15,000 which is something I didn’t really expect, despite the huge amount of interest there was in this item.
“The item relating to Collins also sold extremely well. Throughout the last few months, we have sold a number of interesting items belonging to Collins including a walking stick and a lock of his hair earlier this year! I knew that there would be a great amount of global interest in the flag that we had for sale this time and the bidding didn’t disappoint.
“At Bloomfield Auctions, we have become synonymous with selling historical items from all across Ireland which serve to capture the turbulent periods this island has experienced. That’s why we believe that sales like these are so important – they’re a fantastic way of remembering and indeed treasuring the past.”