In a joint statement, the companies said the deal would create "a stronger, more efficient global provider better able to compete in the rapidly changing office solutions industry".
The combined company would have had combined revenues of about $18 billion in 2012, the firms said.
Under the terms of the all-stock deal, Office Depot will issue 2.69 shares for each OfficeMax share. That is equal to about $13.50 per share, based on Office Depot's closing share price on Tuesday of $5.02.