Metal/ligand in situ assembly is crucial for tailoring the reactivity & selectivity in transition metal catalysis. Cooperative catalysis via a single metal/two ligands is still underdeveloped, since it is rather challenging to harness the distinct reactivity profiles of the species generated by self‐assembly of a single metal precursor with a mixture of different ligands. Herein, we report a catalytic system composed of a single metal/two ligands for a three‐component reaction of polyfluoroarene, α‐diazo ester, and allylic electrophile, leading to highly efficient construction of densely functionalized quaternary carbon centers, that are otherwise hardly accessible. Mechanistic studies suggest this reaction follows a cooperative bimetallic pathway via two catalysts with distinct reactivity profiles, which are assembled in situ from a single metal precursor and two ligands and work in concert to escort the transformation. A cooperative bimetallic catalysis via one‐metal/two‐ligands in situ assembling is developed in geminal polyfluoroarylation‐allylation of diazo esters, delivering products bearing a 1,1′‐aryl, polyfluoroaryl quaternary carbon center. Detailed mechanistic investigation disclosed unique roles of two distinct ligands, suggesting two in situ formed Pd complexes display different reactivities and work cooperatively in two catalytic cycles.