<p>Heterogeneous photocatalysis offers a promising route for solar-to-chemical energy conversion, yet its efficiency continues to be constrained by rapid electron-hole recombination and sluggish surface redox kinetics. Recent advances show that integrating external stimuli, such as electric, magnetic, thermal, microwave fields, can provide dynamically tuneable driving forces that influence charge, spin, and lattice behaviour in semiconductors. These external-stimuli interactions enable new mechanisms for promoting charge carrier separation, stabilising intermediates, and modulating interfacial energetics beyond the limits of conventional band-structure engineering. This review presents a comprehensive discussion of external-stimuli-assisted heterogeneous photocatalysis. We examine how different fields interact with semiconductors through various pathways. Representative material platforms, including metal oxides, polar-faceted supports, two-dimensional chalcogenides, are analysed to reveal structure-activity relationships. We further discuss emerging synergistic effects in multi-stimuli systems, where coupled fields create non-linear enhancements in photocatalytic performance. Advances in operando characterisation techniques are highlighted as essential tools for probing these dynamic processes. Together, these developments illustrate how external stimuli can be harnessed to design adaptive, field-responsive photocatalytic systems capable of significantly higher activity, selectivity, and stability. By outlining mechanistic principles, material design strategies, and key challenges, this review provides a framework for developing next-generation solar-to-chemical energy technologies.</p>