Thermoelectric (TE) modules undergo performance degradation and mechanical failure due to thermal cycling. In the present study, TE modules are subjected to thermal cycling, and the thermoelectric performance is evaluated at periodic intervals. Both the thermoelectric figure of merit, ZT, and the individual components of ZT are measured at each interval. The thermopower and thermal conductivity are measured using steady state infrared microscopy, and the electrical conductivity and ZT are evaluated using a variation of the Harman technique. These properties are tracked over many cycles until device failure. Critical failure occurred after 45,000 thermal cycles, and the mechanical failure of the TE module is analyzed using high-resolution infrared microscopy and scanning electron microscopy. These results quantify the effect of thermal cycling on a commercial TE module performance and provide insight into the packaging of a complete TE module for reliable operation.