Cocatalyst　is　of　paramount　significance　to　provide　fruitful　active　sites　for　suppressing　the　spatial　charge　recombination　toward　boosted　photocatalysis.　Up　to　date,　exploration　of　robust　and　stable　cocatalysts　is　remained　challenging.　Inspired　by　the　intrinsic　merits　of　single-atom　catalysts　(SACs),　such　as　distinctive　electronic　structure　and　high　atomic　utilization　efficiency,　single-atom/transition　metal　chalcogenides　(TMCs)　is　utilized　as　a　model　to　synthesize　CdS-Pd　single-atom　catalyst　(CdS-PdSA)　heterostructures.　This　demonstrates　the　precise　anchoring　of　isolated　metal　single-atom　catalysts　(SACs)　onto　TMCs　through　a　simple　yet　effective　wet-chemical　strategy.　The　resulting　heterostructures　exhibit　significantly　enhanced　and　stable　photocatalytic　activity　for　selective　anaerobic　organic　transformations　and　hydrogen　production　under　visible　light.　This　enhancement　is　primarily　inferred　due　to　the　role　of　Pd　SACs　as　electron　pumps,　which　directionally　trap　the　electrons　photoexcited　over　CdS,　accelerating　the　spatial　charge　separation　and　prolonging　the　carrier　lifespan.　The　charge　transport　route　and　photocatalytic　mechanism　are　elucidated.　This　work　underscores　the　potential　of　SACs　as　cocatalysts　in　heterogeneous　photocatalysis,　offering　valuable　insights　for　the　rational　design　of　atomic-level　cocatalysts　for　solar-to-chemical　energy　conversion　and　beyond.　Metal　single　atoms　act　as　electron　pumps　to　expedite　the　unidirectional　electron　transfer　from　the　TMCs　matrix　to　the　metal　single　atoms,　contributing　to　the　markedly　augmented　organic　transformation　and　hydrogen　generation　activities.　image