Photocatalytic hydrogen peroxide (H₂O₂) generation from oxygen and water using a polymeric photocatalyst is a promising method for solar to chemical energy transformation. Here, we report the hydrothermal synthesis of anthraquinone-based conjugated polymer (ACP) nanoparticles (NPs) for efficient H₂O₂ generation. This synthesis avoids the use of a metal-based catalyst. Anthraquinone (AQ) is crosslinked to resorcinol units of the polymeric chains via a methylene linker to obtain ACP NPs. In the polymeric framework, AQ acts as an acceptor (A), whereas resorcinol acts as a donor (D) through its benzenoid/quinoid forms. The arrangement of donor–acceptor units in the polymeric framework and π-stacked aromatic structure resulted in a broad range of visible light absorption with a low bandgap of 1.78 eV. Hydrothermal synthesis produced ACP as uniformly grown globular-shaped particles with an average size of ∼450 nm. The ACP photocatalyst demonstrated high activity of H₂O₂ generation with a solar-to-chemical energy conversion efficiency of 1.92% in pure water without a sacrificial proton donor. We could achieve a 28.09 millimolar concentration of H₂O₂ after 20 h irradiation in pure water under ambient conditions with an initial rate of H₂O₂ generation of 6097 μmol g⁻¹ h⁻¹. This concentration is almost sufficient for direct use in single-compartment H₂O₂ fuel cells.