The Pd-catalyzed N-arylation method for the synthesis of eighteen N,1-diaryl-1H-tetrazol-5-amine derivatives is reported. By running the reactions at 35 °C, compounds were isolated as single isomers since the undesired Dimroth rearrangement was completely suppressed. Furthermore, the Dimroth rearrangement of N,1-diaryl-1H-tetrazol-5-amines was rationalized by conducting comprehensive experiments and NMR analysis as well as density functional theory (DFT) calculations of thermodynamic stability of the compounds. It was established that the Dimroth rearrangement is thermodynamically controlled, and the equilibrium of the reaction is determined by the stability of the corresponding isomers. The mechanism was investigated by additional DFT calculations, and the opening of the tetrazole ring was shown to be the rate-determining step. By maneuvering Pd-catalyzed N-arylation and the subsequent Dimroth rearrangement, two more N,1-diaryl-1H-tetrazol-5-amine derivatives were acquired, which otherwise cannot be synthesized by employing the C-N cross-coupling reaction.