Julian Assange said the move is part of digitizing secret and once-secret documents from U.S. diplomatic history, the British newspaper The Independent reported Monday.
The Independent said Assange has done much of the work digitizing the material while holed up in the Ecuadorian Embassy in London where he has been staying since last summer.
Assange said the records highlighted the "vast range and scope" of U.S. influence around the world.
The data released Monday on the whistle-blowing website contains more than 1.7 million U.S. diplomatic records from 1973 to 1976, including cables, intelligence reports and congressional correspondence.
Assange said WikiLeaks had been working for about a year on assessing the archived data before releasing it in a searchable form.
The Ecuadorian government gave Assange political asylum after he sought refuge at the embassy in June over fears he would be sent to the United States if he were extradited to Sweden for questioning on sexual-assault claims by two women.
He has denied the charges.