Thermal management of lithium ion battery is a crucial aspect in holistic battery management system (BMS), and the real-time estimation of internal thermal distribution in each battery cell is the key to successful thermal management. In this paper, a physics-based thermal-electrochemical model integrated with actions of electrode reaction, joule heating, heat conduction and heat convection is developed to predict the internal temperature of a battery cell in real time by relying on only the non-intrusive measurements of cell surface temperature and electrical quantities. The modeling approach started from the microscopic electrochemical reaction in the battery interior and ended up with the macro distribution of temperature throughout the cell, with the potential of application in BMS. The temperature distribution of a battery cell under a constant discharge rate has been simulated using the proposed model. The simulated results have been validated by comparison with experimental data.