Searching for d0 magnetism in two-dimensional materials has attracted great attention because of its importance for next-generation spintronics. In this work, doping with pnictogen (X = P and As) atoms is proposed for engineering the magnetic properties of a SnI2 monolayer. The pristine monolayer is a nonmagnetic semiconductor with a band gap of 2.03 eV. Magnetic states are induced by doping with a single pnictogen atom, where an overall magnetic moment of 2.00 mB is produced primarily by the impurity. In addition, the emergence of magnetic semiconducting behavior and in-plane magnetic anisotropy (IMA) is also confirmed. The study of spin coupling in pnictogen-doped SnI2 systems demonstrates the effectiveness of X–X separation for controlling the electronic and magnetic properties. Specifically, an antiferromagnetic semiconducting nature is found to be stable with a small interatomic distance, while increasing the separation between the impurities induces a transition in the electronic behavior, resulting in ferromagnetic half-metallicity or ferromagnetic semiconducting character. In the latter case, large Curie temperatures of 282.20 and 462.66 K are obtained by P and As doping, respectively, indicating the robustness of the ferromagnetism. In addition, the X–X separation also significantly influences the magnetic anisotropy of the doped system. Specifically, perpendicular magnetic anisotropy (PMA) is obtained when two impurities are close to each other, whereas increasing the distance between them induces a PMA-to-IMA transition. Our findings provide insights into the electronic and magnetic properties of the SnI2 monolayer upon doping with pnictogen atoms, suggesting that these efficient doping approaches can induce d0 magnetism and enable promising applications in magnetic-field sensing and magnetoresistive random-access memory (MRAM) fabrication.