The FCC said the merger would accelerate development of a 4G LTE system across the country.
"We anticipate that the combination of T-Mobile USA and MetroPCS would enable the deployment of a substantial LTE network nationally that would enhance competition and provide important benefits for consumers," the commission said in its ruling.
"With today's approval, America's mobile market continues to strengthen, moving toward robust competition and revitalized competitors," FCC Chairman Julius Genachowski said in a statement.
PCMagazine reported that MetroPCS shareholders now have to approve the deal. They are scheduled to vote on the merger at a shareholder meeting on April 12.