"Hillary is going to run," Buffett said at Fortune magazine's Most Powerful Women Summit in California.
"Hillary is going to win," he added. "I will bet money on it, I don't do that easily."
Clinton, who turns 67 on October 26, is widely expected to announce her candidacy for the 2016 presidential elections at the start of next year.
"She's going to announce it as late as possible," Buffett said.
He didn't have any particular predictions about who would win the Republican nomination.
During his 2012 campaign, Obama urged Congress to adopt the "Buffett Rule," which would require a tax rate of at least 30 per cent for incomes over USD 1 million.