Abstract Downsizing the graphdiyne (GDY) network to shape quantum dots (QDs) will provide attractive optical and electronic properties associated with quantum confinement and edge effects. Here, it is demonstrated that quantum confinement and defect introduction allow using GDY in donor–acceptor photocatalytic systems for solar‐to‐hydrogen conversion. The defect‐rich GDY QDs (GDYO‐QDs) exhibit a blue‐to‐green excitation‐dependent photoluminescence behavior, demonstrating their ability to harvest light over a wide energy range. Quantum‐chemical calculations evidenced an increase in the electronic bandgap of GDY upon quantum confinement and defect introduction without the appearance of trap states that can hamper charge transport properties. Such a unique optical behavior of QDs is used in photocatalytic hydrogen generation through the hybridization with TiO 2 as a model photocatalyst. Theoretical and experimental results demonstrate that the donor−acceptor system tremendously boosts the photocatalytic performance, reaching 5288 µmol g −1 after 4 h of illumination at a constant rate of 1322 µmol g −1 h −1 , using a low volume of a sacrificial electron donor (6% v/v). The QDs act as efficient chromophores harvesting UV and visible light while injecting electrons into the TiO 2 . This work opens a new area of using GDYO‐QDs as an efficient chromophore in developing donor–acceptor systems for photocatalysis and future photovoltaic devices.