Atomically　precise　metal　nanoclusters　(NCs)　for　use　as　photosensitizers　in　photocatalysis　have　attracted　considerable　attention　due　to　their　quantum　confinement　effect,　unique　atom-stacking　fashion,　and　enriched　catalytic　active　sites,　which　make　them　promising　photosensitizers　for　solar　energy　conversion.　However,　current　works　on　metal　NC-based　photocatalytic　systems　are　still　in　their　infancy　owing　to　the　complex　synthetic　strategies　of　metal　NCs　and　deficiency　of　metal　NCs　with　a　favorable　energy　level　configuration,　which　substantially　limit　the　exploration　of　metal　NC　photocatalytic　systems,　while　the　photocatalytic　mechanism　remains　elusive.　Herein,　we　conceptually　demonstrate　the　construction　of　a　metal　NC/transition　metal　chalcogenide　(TMC)　binary　heterostructure　photosystem　via　electrostatic　self-assembly　under　ambient　conditions,　wherein　Ag25(SR)18　NCs　(SR:　2,4-dimethylbenzenethiol)　were　precisely　and　uniformly　anchored　on　the　surface　of　TMCs　to　function　as　light-harvesting　antenna.　We　ascertained　that　advantageous　charge　transfer　between　the　TMCs　and　Ag25(SR)18　NCs　resulted　in　a　prolonged　charge　lifetime　and　increased　carrier　density.　Therefore,　self-assembled　metal　NCs/TMCs　heterostructures　demonstrated　significantly　improved　and　versatile　photoactivities　toward　the　anaerobic　photoreduction　of　aromatic　nitro　compounds　to　amino　derivatives　and　heavy　metal　ion　(Cr6+)　reduction　under　visible　light.　Our　work　clarifies　the　photocatalytic　mechanism　of　atomically　precise　metal　NC　photocatalysis　and　opens　up　new　avenues　for　smartly　mediating　the　charge　transfer　and　separation　of　metal　NCs　for　solar　energy　conversion.　©　2024　The　Royal　Society　of　Chemistry.