We report detection of the binary companion to the millisecond pulsar J2302+4442 based on the deep observations performed with the Gran Telescopio Canarias. The observations revealed an optical source with r' = 23.33 ± 0.02 and i' = 23.08 ± 0.02, whose position coincides with the pulsar radio position. By comparing the source colour and magnitudes with the white dwarf cooling predictions, we found that it likely represents an He or CO-core white dwarf and estimated its mass of 0.52^{+0.25}_{-0.19} M⊙ and effective temperature of 6300^{+1000}_{-800} K. Combining our results with the radio timing measurements, we set constraints on the binary system inclination angle i = 73^{+6}_{-5} deg and the pulsar mass m_ p = 3.1^{+2.7}_{-2.0} M⊙.