A thermal management system for a vehicle may include a battery line connected to a high-voltage battery core, provided with a first radiator, and through which coolant is communicated by a first pump; an indoor heating line connected to a heating core for indoor air conditioning, provided with a hydrothermal heater therein, provided with a second pump to fluidically-communicate the coolant, and provided with a first valve at a downstream point of the heating core; a first and a second battery heating line branched or joined at the downstream point of the heating core in the indoor heating line to be connected to the upstream point and the downstream point of the high-voltage battery core, respectively; and a refrigerant line provided with an expansion valve, a cooling core for indoor air conditioning, a compressor, and a condenser.