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.
"In the past decade, with the growth of the internet, our industry has changed dramatically," said Neil Austrian, chairman and chief executive of Office Depot. "Combining our two companies will enhance our ability to serve customers around the world, offer new opportunities for our employees, make us a more attractive partner to our vendors, and increase stockholder value."
Ravi Saligram, president and chief executive of OfficeMax, said: "Together, we will have the opportunity to build on our strong digital platforms and to expand our multichannel capabilities to better serve our customers and to compete more effectively."