The rational synthesis of single‐layer noble metal directly anchored on support materials is an elusive target to accomplish for a long time. This paper reports well‐defined single‐layer Pt (Pt‐SL) clusters anchored on ultrathin TiO2 nanosheets—as a new frontier in electrocatalysis. The structural evolution of Pt‐SL/TiO2 via self‐assembly of single Pt atoms (Pt‐SA) is systematically recorded. Significantly, the Pt atoms of Pt‐SL/TiO2 possess a unique electronic configuration with PtPt covalent bonds surrounded by abundant unpaired electrons. This Pt‐SL/TiO2 catalyst presents enhanced electrochemical performance toward diverse electrocatalytic reactions (such as the hydrogen evolution reaction and the oxygen reduction reaction) compared with Pt‐SA, multilayer Pt nanoclusters, and Pt nanoparticles, suggesting an efficient new type of catalyst that can be achieved by constructing single‐layer atomic clusters on supports.