In this paper, the magnetic effect on micropolar nanofluid flowing in the case of combined convection from a horizontal circular cylinder is investigated at a constant wall temperature. Two commonly applied oxides of metal and nonmetal nanoparticles are immersed in two host liquids: carboxymethyl cellulose-water and kerosene oil. The governing system is converted into a nonlinear system via similarity transformations and then numerically solved using the Keller-box technique. In light of the nanoparticles’ and host fluid’s thermos-physical characteristics, numerical outcomes for the extent of the impact of critical related parameters on temperature, angular velocity, velocity, skin friction, and local wall temperature are obtained, analyzed, and discussed. Furthermore, a comparison with previously published numerical findings on the Newtonian fluid in certain instances was performed. The results reveal that raising the value of the combined convection parameter leads to an enhancement of the Nusselt number, skin friction, velocity, and angular velocity while causing a reduction in the patterns of the temperature profile. The use of silicon dioxide nanoparticles results in the greatest local skin friction when compared to aluminum nanoparticles.