Sn-doped MnNiFeO4 ceramic with negative temperature coefficient (NTC) was prepared through the low-temperature solid-phase reaction route (LTSPR), aiming at improving the sintering behavior and modulating the electrical properties. The experimental results of the ceramic powder precursor indicate that the calcination of the ceramic precursors at above ~300 °C is an exothermic process, which contributes to the transition of the ceramic powder from the amorphous phase into the crystal spinel phase; the spinel phase of ceramic powders can be formed initially at ~450 °C and well-formed at ~750 °C. A high densification of ~98% relative densities and evenly distributed grains within an average size of 2~12 μm for the sintered Sn-doped specimen were obtained. The specific resistance and B-value were notably increased from 12.63 KΩ·cm to ~24.65 KΩ·cm, and from 3438 K to ~3779 K, respectively, with the Sn-doping amount. In contrast, the aging rates of the Sn-doped specimen have not changed markedly larger, waving around ~2.7%. The as-designed Sn-doped MnNiFeO4 can be presented as a candidate for some defined NTC requirements.