Recent research demonstrated high thermoelectric figure of merit in CrN, implying that the transition metal nitrides could be promising thermoelectric materials. Herein, we investigate the thermoelectric properties of a newly predicted superhard material WN6 by using first-principles calculations and Boltzmann transport theory. Results indicate that WN6 has a small band gap of 0.76 eV, a relatively low lattice thermal conductivity of around 10.7 W/mk at 700 K, and a large Seeback coefficient of 1330 μV/K at 300 K. Its low lattice thermal conductivity and large Seeback coefficient lead to an excellent thermoelectric response, with the maximum thermoelectric figure of merit being 0.78 for n-type. The mode Grüneisen parameters and phonon mean free path are exhibited to analyze the anharmonic properties and the size effects. These results shed light on the thermoelectric performance of WN6.