Rolls-Royce is also a major beneficiary of the move, which may be worth as much as $8.4bn, as Rolls-Royce offers the only engine available on the Airbus plane.
Meanwhile, 12 Boeing 777 aircraft are also on order, and Emirates said it was committing close to $35bn overall with the deals.
Sheikh Ahmed bin Saeed al-Maktoum, the chairman and chief executive of Emirates, said the airline was "making aviation history".
"This is the largest ever aircraft commitment in civil aviation made by any airline in a single order," he said.
Asked why Emirates chose Airbus over Boeing, Tim Clark, the Emirates president, said: "The 787-9 wasn't suitable for us and the 787-10 wasn't available to us."
Boeing deal 'lost'
The 787 Dreamliner model is due at the end of next year, six months later than planned.
Boeing had 710 orders for the passenger jet as of mid-October, the company's most successful sales effort for a new model.
Boeing has not formally offered the 787-10, a longer-range and bigger version of its 787-9.
Scott Carson, Boeing commercial airplanes' president, conceded that Boeing lost the Emirates order.
He said: "Obviously Boeing would like to win every venture we are involved in ... We didn't have the airplane they wanted at this time."
Airbus has also named Prince Walid bin Talal bin Abdul Aziz al-Saud, a Saudi billionaire, as the first private buyer of the A380.
The prospective buyer's identity had been kept secret for months but was unveiled to coincide with the Dubai air show.
Walid, whose interests span from hotels and financial institutions, has ordered a VIP version of the A380, dubbed the "Flying Palace".
He already owns a Boeing 747-400, the newest type of the original jumbo jet currently in service.