Photocatalysis (PC) and photoelectrocatalysis (PEC) are attractive routes to utilize the abundant solar energy for energy- (H₂ and photo-reformed organics) and environment- (water remediation) related applications. The fundamental challenges with PC and PEC are photon absorption, restricted charge diffusion lengths because of exciton recombination, photo-corrosion, and kinetics of the reactions. These limitations can be addressed by suitable catalyst design with precisely controlled morphology and active sites at the atomic precision. Atomic layer deposition (ALD) is one such efficient route to establish thorough control of photocatalyst fabrication. Thanks to ALD, it is now feasible to synthesize particles, thin films, core–shell structures, and porous and membranous photocatalytic materials with the highest precision and homogeneity. One further challenge is understanding probable reactor designs when exploiting ALD-based coatings. Herein, we reviewed various possible routes to fabricate photocatalysts using ALD with insights of PC/PEC reactions based on particulate, thin film, core–shell, and porous photocatalytic materials. This review also discusses the importance of translating the underlying reaction mechanisms to scale-up the reactor design with respect to the ALD approach. Initially, basic PC and PEC mechanisms for energy and environmental applications using growth-controlled ALD catalyst systems are given attention. Subsequently, more insights on microscale reactor combinations with ALD over-coatings and the challenges in transforming such microscale systems to the macroscale are discussed. Finally, the prospects of ALD for large-scale systems and the corresponding influential factors, such as high residence time scales, bandgap engineering, light penetration, and deposition thickness for PC and PEC applications, are examined in detail.