The present analysis deals with the heat transfer of chemically reactive magnetic-nanofluid over a stretching surface by considering the aligned magnetic field in a porous medium under the influence of nonlinear thermal radiation, variable thermal conductivity and suction. An isothermal model of homogeneous–heterogeneous reactions is used to regulate the solute concentration profile. It is assumed that the water-based nanofluid is composed of single and multi-walled carbon nanotubes. By applying a suitable set of similarity transformations, the system of partial differential equations is first transformed into a system of nonlinear ordinary differential equations before being solved numerically. The impact of various pertinent parameters on the velocity, temperature, concentration, skin friction and local Nusselt number coefficient is discussed. It is found that the increase in the rate of heterogeneous and homogeneous reactions retards nanoparticle concentration distribution. The existence of variable thermal conductivity and an inclined magnetic field realise a decrease in heat transfer.