Mr Nixon, who was a senior analyst with the CIA, has now written a book about his encounter with the man who had been in power in Iraq for more than 20 years.
In an article in Time magazine, Mr Nixon writes: "When I interrogated Saddam, he told me:
'You are going to fail. You are going to find that it is not so easy to govern Iraq.'
"When I told him I was curious why he felt that way, he replied: 'You are going to fail in Iraq because you do not know the language, the history, and you do not understand the Arab mind.'"
Mr Nixon says some of what the Americans thought before the Iraq War started in March 2003 was wrong.
"I heard over and over from counterparts in the military and the Bush administration that if we caught Saddam we would be able to nip the growing Iraqi insurgency in the bud.
"This presupposed that Saddam had an iron-like control over the Sunni insurgency (he didn't) and that decapitating the Baathist regime would make Iraq a peaceful country (it didn't).
"This was the underlying ethos of the Bush administration's decision to launch Operation Iraqi Freedom."
In his book, Mr Nixon ponders what might have happened had Saddam remained in power