Mg3Bi2-vSbv (0 <= v <= 2) is a class of promising thermoelectric materials that have a high thermoelectric performance around room temperatures, whereas their thermoelectric properties under pressures and temperatures are still illusive. In this study, we examined the influence of pressure, temperature, and carrier concentration on the thermoelectric properties of Mg3Bi2-vSbv using first-principle calculations accompanied with Boltzmann transport equations method. There is a decrease in the lattice thermal conductivity of Mg3Sb2 (i.e., v = 2) with increasing pressure. For a general Mg3Bi2-vSbv system, power factors are more effectively improved by n-type doping where electrons are the primary carriers over holes in n-type doping, and can be further enhanced by applied pressure. The figure of merit (zT) exhibits a positive correlation with temperature. A high zT value of 1.53 can be achieved by synergistically tuning the temperature, pressure, and carrier concentration in Mg3Sb2. This study offers valuable insights into the tailoring and optimization of the thermoelectric properties of Mg3Bi2-vSbv.