In this paper, the thermo-viscous fingering instability in the displacement of Newtonian fluid by a shear-thinning non-Newtonian fluid in the heterogeneous porous media is studied. Here, the heterogeneity of medium is assumed to be layered. Two different types of displacements are considered: a cold low viscous fluid displaces a hot high viscous one and vice versa. The numerical solution is obtained using a spectral method based on Hartley transforms and fourth-order Adams-Bashforth technique. By interoperation of concentration and temperature contours, transversely averaged profiles, mixing length, and sweep efficiency, it is shown that heterogeneity of porous media has a significant effect on the thermo-viscous fingering instability. The decreasing thermal-lag coefficient leads to more unstable flow and Lewis number has different effects on displacements. When a cold less viscous fluid is displacing fluid, this parameter has destabilizing effect while for displacing hot more viscous fluid, and it acts in favor of stability.