He made the comments in a discussion at The Institute for National Security Studies in Tel Aviv, Israel.
According to the reporter, Petraeus said Snowden has revealed enormous amounts of information about intelligence-gathering methods.
Petraeus added that Snowden did "the most damage of any spy, turncoat, whatever,” the New York Times’ Jerusalem bureau chief tweeted.
Snowden, a former contractor for the National Security Agency, has been leaking government documents since last June to the media. The documents have revealed the scope of the agency's domestic and global surveillance programs, which eventually prompted President Obama to announce reforms earlier this month.
Petraeus served as director of the CIA from September 2011 until his resignation in November 2012. He stepped down after revelations came out about his extramarital affair. Petraeus also served as the U.S. military commander in Iraq and Afghanistan.
Last year, he was appointed to be a visiting professor at CUNY’s Macaulay Honors College in New York.