Abstract The controllable synthesis of phosphorus (P) doped noble metal electrocatalysts with a well‐defined structure and composition has attracted sufficient attention in energy chemistry. In this study, atomic‐level P‐doped Pt nanodendrites (PtP NDs) with tunable composition and highly branched architecture are successfully prepared by post‐phosphating reaction of sodium hypophosphite monohydrate at room temperature. Due to its electrophilic properties, P effectively regulates the electronic structure of the d‐orbitals of Pt. The charge change induced by P on a local scale can effectively regulate the selective adsorption of electrocatalytic reaction intermediates. The electrocatalytic results show that the η 10 value of PtP NDs in hydrogen evolution reaction is only 13.3 mV, and the mass activity of PtP NDs in methanol oxidation reaction is 4.2 A mg −1 , which is 3.8 times larger than that of commercial Pt/C. Most importantly, the atomic‐level P doping greatly improves the stability of PtP NDs, which is crucial to facilitating the catalysts’ commercialization process.