The use of nanofluid technology as a working fluid in specific channels has significantly improved heat exchange rate in thermal engineering applications. In fact, nonuniform channels with converging or diverging nature offer special characteristics that encourage the most favorable usage, such as flow via nozzles, diffusers, and reducers in polymer processing and flow through canals and rivers. Therefore, we present a theoretical and mathematical insight into nanofluid heat transfer and flow dynamics in nonuniform channels utilizing non-Newtonian nanofluids. The impacts of heat absorption/generation and Joule heating in a magnetohydrodynamics (MHD) flow of Carreau nanofluids with viscous dissipation are addressed in this research. Brownian and thermophoresis diffusion are deliberated to investigate heat and mass transport mechanisms. The modeled flow equations are numerically handled using a built-in MATLAB code based on the finite difference approach (bvp4c) for velocity, temperature, and concentration fields. The consequences of the variable magnetic field, heat absorption/generation, and numerous physical parameters on the temperature and concentration field are surveyed. The results indicate that the increasing values of heat generation/absorption parameter and Eckert number significantly enhances the temperature profiles in convergent channel. In addition, a similar behavior is observed for higher Prandtl number. An assessment of solutions achieved in this article is made with existing data in the literature.