The effects of Joule heating and viscous dissipation on the two-dimensional Carreau fluid flowing through a stretching sheet with variable thickness are inspected with the supposition of slip parameters. The leading equations are altered as a set of (nonlinear) ordinary differential equations by means of proper similarity alterations. With the assistance of shooting procedure, subsequent equations are unravelled numerically. The impacts of appropriate parameters such as Weissenberg number and slip parameters (related to velocity and temperature) on the common profiles (velocity, concentration and temperature) are analysed via graphs. And also, we have analysed the effects of the identical parameters on skin friction coefficient and rate of transfers (heat and mass) by means of tables. From the outcomes, we observed that (a) the velocity slip parameter lowers the velocity but boosts the friction factor, (b) Weissenberg number boosts the velocity but shows conflicting behaviour on temperature, and (c) all boundary layers are observed to be thinner against wall thickness parameter. So, it benefits to improve both transfer rates (heat and mass), (d) the concentration boundary layer is observed to be thinner during chemical reaction, (e) magnetic field parameter and Eckert number are both reduce the local Nusselt number, and (f) wall thickness parameter and chemical reaction parameter are both improve the rate of mass transfer.