The move was announced on Thursday at the annual meeting of the Western and Central Pacific Fisheries Commission meeting in Manila.
The meeting also decided to take measures to protect whale sharks from tuna nets.
"At more than 4.7 million square kilometres of ocean, this designation doubles the size of the area already protected by all six existing shark sanctuaries," said Josh Reichert, head of the Pew Environment Group on Friday.
But, he said, "sharks are threatened throughout much of the world's oceans, and there is a great need to protect them before they slip below levels from which they may never recover".
About 73 million sharks are killed every year for, mainly for their fins, according to the WWF.
A third of shark species are now categorised as threatened or near-threatened.
The European Union has had a ban on finning since 2003 and extended a total ban on fishing for endangered shark species for two years in November.
Shark fishing was revived in the waters off the French Indian Ocean island of Réunion this year after a spate of attacks on surfers.