Single-atom catalysts (SACs) present a promising subclass of classic heterogeneous catalysts by maximizing metal dispersion and enhancing efficiency. Although high-density SACs (HD-SACs) are reported, their synthesis is typically constrained to specific metal-support combinations and high-temperature annealing, limiting their translation to wider applications. Herein, a universal bottom-up approach for the preparation of mono- and bimetallic HD-SACs based on the polycondensation of 1,2,4,5-benzenetetramine with a wide range of metal monomers containing 1,10-phenanthroline-5,6-dione ligands is introduced. The synthesized materials are atomically dispersed and exhibit metal loadings up to 27.5 wt% with high structural stability. Their versatility as catalysts is explored in electrocatalytic and photocatalytic applications. The materials exhibit remarkable stability under operational conditions. Furthermore, this synthetic strategy is scaled up and automated, demonstrating the robustness and reproducibility and laying the groundwork for self-optimizing data-driven materials discovery.