Transient Liquid Phase Bonding (TLP) is a high temperature joining process that is used for bonding advanced materials that are generally difficult to weld by conventional welding techniques. This study is designed to adequately examine the effect of the key process parameters, such as the bonding time and temperature, on the kinetics of isothermal solidification during TLP bonding. The TLP bonding experiments are carried out in a vacuum furnace under a vacuum pressure of 5 x 10-5 torr at temperatures of 790°C, 820°C, and 850°C. The results show that a deviation from the parabolic law occurred during the isothermal solidification process, at all the selected bonding temperatures. This deviation from the parabolic law cannot be explained by the existing concepts suggested in the literature. In this research work, qualitative and quantitative analyses of the concentration profiles of the experimental samples reveal that the diffusion coefficient is a function of concentration and time, which is in contrast to the general assumption of a constant diffusion coefficient. This important experimental finding, which has not been previously reported in the literature during TLP bonding, can explain the occurrence of a deviation from the parabolic law. Furthermore, the experimental results show that an increase in the bonding temperature results in an increase in the rate of isothermal solidification, due to increased diffusivity of the MPD solutes with increase in temperature. Notwithstanding, larger residual liquid is observed at higher bonding temperatures; this is attributed to the overriding effect of the increase in the volume of the liquid phase at the joint when temperature is increased.