This paper reports the investigation on the process of thermally mediated droplet formation at a microfluidic T-junction. The temperature field generated by an integrated heater causes changes in properties of the fluids and affects the droplet formation process. The droplet formation process is formulated in this paper as an incompressible immiscible two-phase flow problem. The motion of the two-phases is strongly coupled by interfacial conditions, which are governed by the three-dimensional Navier-Stokes and the energy equations. The interface or the droplet surface is described by a narrow-band particle level-set method. The numerical solutions of the problem are obtained with finite volume method on a staggered mesh and validated with the experiment data on droplet formation in the dripping regime of a T-junction. The combined effect of the temperature-dependent viscosities and interfacial tension of the fluids results in a larger droplet at elevated temperature. The effectiveness of the penetration of temperature field induced by different heater geometries that resulted in different incremental change in droplet size over a temperature range is discussed.