Many studies have been performed on non-Newtonian fluid flow through the nonuniform stretching sheet. In most cases, the problem is assumed to be two-dimensional fluid flow and a similarity solution is exploited. In this paper, we consider the effect of viscous dissipation on the MHD non-Newtonian fluid flow and heat mass transfer due to slendering stretching sheet with thermal radiation. Both Williamson and Casson models are opted here while the mathematical modeling is used for the principle flow equations. By dimensionless transformation, the governing equations are transformed to identically coupled three equations along with three common boundary conditions imposed. They are then solved numerically by using Chebyshev spectral method for different values of the physical parameters involved. These governing parameters are graphically shown to have a considerable influence on the fluid flow and heat mass transfer characteristics of this model. Local heat transfer rate is found to depend on both magnetic parameter and Casson parameter in addition to the Eckert number dependence. Likewise, due to increase of Casson parameter, the sheet temperature and the thermal boundary layer thickness enhances and also the same behavior is observed for increasing the radiation parameter.