Chiral photodetectors, optoelectronic devices that can detect circularly polarized light (CPL), have attracted much attention as building blocks of next-generation information technology. However, their performance has been severely limited by the tradeoff between the external quantum efficiency (ηE) and the dissymmetry factor of photocurrent, the latter typically being limited by the small dissymmetry factor of absorption (gA). This work numerically demonstrates that a circular polarization-sensitive organic photodetector (CP-OPD) based on a chiral plasmonic nanocavity can achieve both high ηE and gA. The design of the chiral nanocavity, featuring a circular dichroic plasmonic mode with a high photonic density of states in the subwavelength thick photoactive layer, is decoupled with that of the photoactive layer, which enables the independent control of the circular dichroic and photon-to-charge conversion properties. By investigating the interaction between CPL and the molecules constituting the photoactive layer, a design principle of the plasmonic CP-OPD is established, resulting in superior performance with ηE = 23.8 % and gA = 1.6.