We studied thermoelectric properties of intrinsic, n- and P-type bismuth telluride nanowires with the growth direction [110]. The dependences of the thermoelectric parameters on nanowire thickness, gate voltage, and excess hole (electron) concentration were investigated in the constant relaxation-time approximation in the temperature range from 77 to 500 K. The results of our analysis show that both the electric field effect and size quantization effect lead to enhancement of the thermoelectric figure of merit. The external electric field can increase the Seebeck coefficient of the bismuth telluride nanowires with thicknesses of 7 and 15 nm by nearly a factor of 2 and enhance the thermoelectric figure of merit by an order of magnitude. The EFE can effectively control the type of the NW conductivity by adjusting the charge carrier concentration. It compares favorably with the doping effect because the number of scattering centers is not changed under the electric field bias. For the 7-nm-thick (15-nm-thick) intrinsic and 15-nm-thick p-type NWs, under the applied electric field, the maximum absolute values of the Seebeck coefficient of 342 (302) and 267 μV/K are achieved at a temperature of 400 (325) and 390 K, correspondingly. The confinement effect on the electron density of states leads to an increase in the NW Seebeck coefficient, while the increase in the carrier concentration causes the decrease in S. The applied electric field permits decreasing the NW thermal conductivity.At the room temperature, for the 7- and 15-nm-thick P-type (intrinsic) nanowires, the maximum value of the figure of merit is 3.1 (3.4) and 1.48 (2.4), correspondingly, under the applied electric field.