Bi0.5Na0.5TiO3 (BNT) exhibits relatively high spontaneous polarization near room temperature and is therefore regarded as a promising lead-free pyroelectric platform. However, its room-temperature pyroelectric coefficient remains relatively low, while polarization readily decays under cyclic external fields or thermal perturbations, thereby limiting practical applications. This work introduces an A/B-site synergistic high-entropy component, (Bi1/3Na1/3Ba1/3)(Ti5/6Ga1/12Sb1/12)O3 (BNBTGS), forming a (1 − x)BNT-xBNBTGS solid solution to regulate the polarization structure and relaxation behavior. The compositional disorder introduced at the A/B-site induces lattice distortion and octahedral tilting, thereby promoting local structural heterogeneity and polarization rearrangement. These effects establish a tunable coexistence of R3c and P4bm phases, increase the density of polar nanoregions (PNRs), and refine ferroelectric domains. Consequently, polarization becomes more responsive to electrical and thermal stimuli, accompanied by a reduction in the switching barrier and a consequent increase in dP/dT. For the optimized composition (x = 0.14), the room-temperature pyroelectric coefficient (pRT) increases from 1.25 × 10−8 to 4.04 × 10−8 C cm−2 K−1, while the temperature of the pyroelectric peak decreases from 160 °C to about 100 °C, enabling a stronger pyroelectric response at lower temperature. Thermal cycling further confirms the excellent stability, with current fluctuations below 2%. This work elucidates the high-entropy-induced polarization evolution mechanism and provides a new design strategy for optimizing the pyroelectric performance of lead-free ceramics.