Efficient mass transfer and light utilization are essential for high photocatalytic production rates. Here, we present a hierarchical three-dimensional (3D)-printed aerogel photocatalyst that unites both aspects by taking inspiration from the light scattering in clouds during photochemical processes and from mass transfer in plants during photosynthesis. We combine the geometric freedom of additive manufacturing with computational fluid dynamics and Monte Carlo simulations to guide the implementation of a self-supported aerogel in a continuous gas flow reactor. Here, 3D microstructuring reduced the pressure drop of a monolithic aerogel by 5 orders of magnitude without compromising the gas permeation and the light-harvesting efficiency of the intrinsic nanoporous material. We match the macroscopic thickness with the ultraviolet (UV) light penetration depth and show that the 3D aerogel of 1.1 mm thickness improves photocatalytic hydrogen production rates relative to the nanoparticle powder by a factor of five from 1.3 to 6.6 μmol g^-1h^-1for TiO₂and from 30.0 to 141.8 μmol g^-1h^-1for Au/TiO₂, respectively. Ultimately, our approach can be applied for other nanomaterials to boost the overall performance of a variety of photochemical processes and reactor designs.