A plasma-assisted staged combustor that can reduce NOx generation is introduced. This combustor is based on a commercial combustor. Only the internal structure of the commercial combustor head was modified to introduce staged combustion and plasma into the combustor. The outer frame and configuration of the combustor remain unchanged. Staged combustion adopts successive fuel-rich and fuel-lean flames to achieve low NOx combustion. However, this can cause flame instability. In the proposed combustor, plasma was adopted for stable operation of the first-stage combustor. The proposed combustor recorded lower NOx generation than a prototype combustor, and three different mechanisms that affected this NOx reduction in the staged combustor were analyzed. Plasma-stabilized fuel-rich flame in the first-stage combustor and hydrogen from the rich flame played a key role for NOx reduction. Plasma appears to be a prominent tool for flame stabilization under the harsh conditions of a combustor for low NOx applications.