Converter IGBT valve plays a vital role in deciding the efficiency and reliability of the UPFC. The efficiency of UPFC is a function of Thermal losses, conduction losses, and switching losses that occur in the IGBT valve. Junction temperature influences the failure rate of the converter valves, which in turn affects the reliability of the converter. A novel technique to evaluate specific valve failure rate, by directly considering the thermal losses that impact on the failure rate, is proposed and implemented for 48 pulse converter-based UPFC. Adaptability to any power electronic valve- based applications, to quantify the valve failure rate, is the significance of the proposed technique. A case study of converter leg with two IGBT valves operating at 12000 Hz, GT30F123 part number is simulated in Piecewise Linear Electrical Circuit Simulation (PLECS). Switching losses, conduction losses, and thermal losses are evaluated by referring to the switching characteristics obtained by PLECS, and the simulation results are validated with analytical values. Reliability Indices such as the probability of attaining hundred percent, fifty percent, and zero percent operating modes are evaluated. Based on probabilities, the frequency of attaining the state probabilities and Mean Time To Failures (MTTF) are derived by developing the Markov model. The quantitative analysis of the thermal losses, failure rate, and lifetime of the UPFC provides a comprehensive picture of the UPFC performance. The proposed valve failure rate evaluation method is more accurate than analytical valve failure rate evaluation techniques.