We provide a quantum derivation of Einstein's Weak Equivalence Principle (WEP) of general relativity using a new quantum gravity theory proposed by the authors called Electro-Magnetic Quantum Gravity or EMQG (ref. 1). Newtonian Inertia is a property of matter due to the strictly local electrical force interactions contributed by each of the (electrically charged) elementary particles of the mass with the surrounding (electrically charged) virtual particles (virtual masseons) of the quantum vacuum. The sum of all the tiny electrical forces (photon exchanges with the vacuum particles) originating in each charged elementary particle of the accelerated mass is the source of the total inertial force of a mass which opposes accelerated motion in Newton's law 'F = MA'. We found that gravity also involves the same 'inertial' electromagnetic force component that exists in inertial mass. We propose that Einstein's general relativistic Weak Equivalence Principle (WEP) originates from common 'lower level' quantum vacuum processes occurring in both inertial mass and gravitational mass, in accordance with the principles of quantum field theory. Gravitational mass results from the quantum activities of both the electrical force (photon exchanges) component and the pure gravitational force (graviton exchanges) component, acting simultaneously on the elementary particles that make up a mass.