Biological assembly processes offer inspiration for ordering building blocks across multiple length scales into advanced functional materials. Such bioinspired strategies are attractive for assembling supported catalysts, where shaping and structuring across length scales are essential for their performance but still remain tremendously difficult to achieve. Here, we present a simple bioinspired route toward supported catalysts with tunable activity and selectivity. We coprecipitate shape-controlled nanocomposites with large specific surface areas of barium carbonate nanocrystals that are uniformly embedded in a silica support. Subsequently, we exchange the barium carbonate to cobalt while preserving the nanoscopic layout and microscopic shape, and demonstrate their catalytic performances in the Fischer–Tropsch synthesis as a case study. Control over the crystal size between 10 and 17 nm offers tunable activity and selectivity for shorter (C5–C11) and longer (C20+) hydrocarbons, respectively. Hence, these results open simple, versatile, and scalable routes to tunable and highly reactive bioinspired catalysts.