Plasmonic enhancement of nonlinear light–matter interaction can be achieved via dedicated optimization of resonant plasmonic modes that are spectrally matched to the different wavelengths involved in the particular nonlinear optical process. Here, the generation and enhancement of broadband four-wave mixing (FWM) are investigated in a plasmonic azimuthally chirped grating (ACG). The azimuthally varying grating periodicity in an ACG offers a well-defined channel to mediate the near field and the far field over a broad range of wavelengths. However, the particular mechanism responsible for field enhancement in such a platform depends on the interplay between the effects manifested by both the groove geometry and the grating’s periodicity. This work delineates the collective contribution of groove geometry-dependent localized surface plasmon resonance and periodicity-dependent plasmonic surface lattice resonance over a broad range of wavelengths to bring into effect the enhancement of broadband FWM in an ACG.