The Trade Commission, which in 1997 blocked the merger of Office Depot Inc. and Staples Inc., said that market conditions have changed since then.
Other retailers have beefed up their office supplies offerings and consumers can also go online, through Amazon, for instance, to purchase supplies, the commission said.
"Our decision highlights that yesterday’s market dynamics may be very different from the market dynamics of today," the commission said in a statement. "In this case, significant developments in the market for consumable office supplies have led us to approve a merger when we had blocked a similar merger sixteen years ago."
The vote to approve the merger was unanimous, 4-0.
The merger, first announced in February, combines office supplies superstores that are among the largest.
Executives at Office Depot and OfficeMax welcomed the news:
“We have been preparing for the integration for the past several months and are delighted that, with this key regulatory milestone now complete, we have taken another step in our path to becoming a combined company,” said Neil Austrian, chief executive of Office Depot.