In this article, we probe the multiple-slip effects on magnetohydrodynamic unsteady Casson nano-fluid flow over a penetrable stretching sheet, sheet entrenched in a porous medium with thermo-diffusion effect, and injection/suction in the presence of heat source. The flow is engendered due to the unsteady time-dependent stretching sheet retained inside the porous medium. The leading non-linear partial differential equations are transmuted in the system of coupled nonlinear ordinary differential equations by using appropriate transformations, then the transformed equations are solved by using the variational finite element method numerically. The velocity, temperature, solutal concentration, and nano-particles concentration, as well as the rate of heat transfer, the skin friction coefficient, and Sherwood number for solutal concentration, are presented for several physical parameters. Next, the effects of these various physical parameters are conferred with graphs and tables. The exact values of flow velocity, skin friction, and Nusselt number are compared with a numerical solution acquired with the finite element method (FEM), and also with numerical results accessible in literature. In the end, we rationalize the convergence of the finite element numerical solution, and the calculations are carried out by reducing the mesh size. Appl. Sci. 2019, 9, 5217 2 of 21 partial velocity slip can occur on the stretching boundary. In an assortment of industry procedures, the influences of slip can crop-up at the boundary of pipes, surfaces, and walls. The Navier Stoke velocity slip conditions are customary to approach in the study of slip phenomenon.There are hundreds of applications in industries and engineering, and magneto-hydrodynamic fluid flows through stretching sheet have achieved much importance in recent days, according to Mabbod et al. [3]. Applications as well as the liquid coating on the photographic films, boundary layers throughout the liquid film in the concentration procedure, and the aerodynamic excrescence of plastic sheets exist. With this, the extensive range of applications of magnetohydrodynamic flow that can be found in copious fields like in electronic cooling process, in boilers, heat lagging, and metal extrusion, geothermal system, nuclear process, micro-magnetohydrodynamic pumps, underground water system, in energy storage units, biological conveyance, and in the thermal energy procedure has played a very important role. Unsteady flow due to the stretching sheet has been scrutinized by Pop and Na [4]. Afterward, Sheridan et al. [5] investigated the significance of variable wall temperature and variable heat flux in the boundary layer flow over the unsteady stretching surface with similarity transformation. An unsteady stagnation point flow of the viscous fluid caused by a stretching sheet under the influence of slip condition has been reported by Bhattacharyya et al. [6]. The impact of the magnetic field on the two-dimensional flow of nano-fluid with and without slip condition was conferred b...