Germany, Israel, the United States signed an agreement to open the files at an official ceremony in Berlin on Wednesday, along with Britain, France, Luxembourg, Greece and Italy.
The agreement will give people access to up to 50 million documents on some 17 million individuals and is expected to shed new light on the Holocaust, in which 11 million people including six million Jews were murdered during World War II.
The archive, housed in the west German town of Bad Arolsen, is the world's biggest collection of documents relating to the Second World War and Hitler's National Socialist party.
The Nazis were meticulous, documenting everything from the mundane, such as how many meals a forced labourer received, to the horrific, in describing a concentration camp prisoner's death in painstaking detail.
Many of the documents inside the cabinets describe basic facts, such as a name on a concentration camp death list.
Others of the archive's 30 million documents relate to mental illness, homosexuality, medical treatment and the presence of head lice.
The decision to open the archive was reached in April by the 11-nation governing body of the International Tracing Service, the arm of the International Committee of the Red Cross that oversees the archive in the western German town of Bad Arolsen.
The service was founded after World War II to trace missing persons.
Under the provisions of a 1955 treaty, third parties had previously only been able to access the archives with the written consent of a victim.
Later, survivors eligible for compensation applied to the archive for documentary evidence of their mistreatment.
Ageing Holocaust survivors and victims' families had pressed for the change, arguing that the histories of their loved ones could otherwise be lost.
"For Germany, the signing underlines the importance it attaches to dealing with the past"
Guenter Gloser, Germany deputy foreign minister
Germany had said that access to the files by Holocaust researchers would violate its privacy laws, however it dropped its objection earlier this year.
Guenter Gloser, the German deputy foreign minister, called the process "long and sometimes cumbersome" but said that in the end, it represents a "big success for researchers".
"For Germany, the signing underlines the importance it attaches to dealing with the past," he said.
Once signed, the protocol still needs to be ratified by most of the 11 signatory states, including Germany and France, before the archives can be opened. The US Congress does not need to ratify the agreement.
Belgium, Poland and the Netherlands are to sign the agreement later on.
There is no concrete timeline on when access will be broadened, but Brigitte Zypries, the German justice minister, has said it would be by the end of the year.