Treatment of well flowlines with thermochemical/exothermic fluid has shown good results for wax removal compared with conventional hot oil, hot water, or solvent treatments. However, the technique has not gained widespread use because of the lack of sufficient scientific publications that can give more insights into its use and help in designing a safe and effective treatment. This paper presents a novel transient mathematical model for the design and analysis of thermochemical treatment for well flowlines by accounting for the chemical kinetics, heat transfer, fusion of wax, and associated two-phase flow. The governing equations have been solved using the finite-volume method. The resulting simulator can be used to prepare an optimum thermochemical plan by analyzing the effects of important factors including wax details, deposition profile, heat loss, formulation composition, and injection strategy. Simulation results obtained with the developed model indicate that the entire filling of flowline with thermochemical fluid is not necessary for complete wax removal. Injection of a small thermochemical spacer (TCS) in the flowline followed by its displacement with crude oil can be sufficient in the case of short flowlines of onshore fields. Selection of initial reactant concentration and pH has to be done judiciously based on the maximum allowed temperature in the flowline and the desired extent of chemical utilization. A sensitivity analysis has shown the existence of an optimum range of injection rate below which wax removal efficiency is compromised by excessive heat loss and above which it is reduced by insufficient residence time. The major limitation of this technique is encountered for large flowlines where a possibility of resolidification of removed wax deposits exists because of excessive heat loss. Flowlines of length less than 5 km are found to be ideal candidates as in that case, sufficiently high temperatures can be maintained throughout the journey of TCS in the flowline, which will prevent resolidification.