The documents, some of which date back to 1943, were gathered by the United Nations War Crimes Commission over six decades ago and were previously sealed to all but a few with special permission.
The files, which will be made available by the London-based Wiener Library with an online-searchable catalog on April 21, provide evidence that the allied forces were aware of the large-scale murders of Jews as early as December 1942, the Independent reports.
The files include "extraordinarily detailed" accounts of victims inside the concentration camps where millions of Jews were gassed, according to the Guardian.
However, despite this knowledge, the allied governments did little to aid those at risk.
Until now, only researchers authorized by both their national governments and the UN's secretary-general were allowed to view the WWII records - without taking any notes or copies.
Author and historian Dan Plesch, who just released a book on the files after studying the documents for a decade, said they are a "huge resource for combating Holocaust denial."
"The German national authorities were never given access to the archive by the allies after the war. All of this has never seen the light of day," Plesch added.The UN agency operated between 1943 and 1948 to help national governments in the trials of WWII war criminals.
"The UN War Crimes Commission catalogue, which can be searched online, will be available through our website this week," said the library's archivist, Howard Falksohn. "People will then be able to come in and look through the archive itself.
"We anticipate a lot of interest. Some of the PDF files each contain more than 2,000 pages. This is the first time they will be available to anyone in the UK. It may well be that people will be able to rewrite crucial chapters of history using the new evidence."