The New York Times said a lawyer involved in the case said Armitage confirmed he disclosed casually to Robert Novak that Valerie Plame worked for the CIA at the end of an interview in his State Department office in 2003.
The Times was unable to reach Armitage for comment.
The leak became hot news, mostly in Washington, and launched a politically laden criminal investigation that went as high as Vice President Dick Cheney's office.
There were allegations the leak was retaliation against Plame for remarks made by her husband, former Ambassador Joseph Wilson, who said the Bush administration had used weak evidence for going to war with Iraq.
Despite the disclosure Armitage was the source, no explanation was given as to why he would mention a covert agent's name to a journalist, or why the journalist would publish it.