Magnetic doping holds a great potential for tailoring material properties of semiconductors via control over exciton-dopant interactions. Hybrid metal-halide perovskites are a new class of high-performance solution-processable semiconductors which combine remarkable optoelectronic performance with tolerance to structural defects and impurities. This thesis demonstrates magnetic doping of lead halide perovskites and investigates the resulting magneto-optical effects on exciton dynamics. We synthesise manganese-doped 2D Ruddlesden-Popper perovskite phenethyl ammonium lead iodide thin films and characterise the material’s basic properties. We report qualitative evidence that, depending on doping concentrations, Mn2+ ions occupy different lattice sites, e.g., either substituting lead or incorporating interstitially, or being phase separated from the host perovskite. We find that this manganese doping induces paramagnetic properties in the otherwise diamagnetic perovskite, due to introduction of Mn2+ ions that carry magnetic moment with S = 5/2 spin state into the perovskite host semiconductor. Employing spin resonance and magneto-optical spectroscopy, we find coupling between the dopant’s magnetic moment and the exciton spin of the semiconductor. We report magnetic brightening of a dark exciton population by state mixing with the bright excitons at cryogenic temperatures. We show that manganese doping leads to a significant enhancement of this effect. For this dark exciton, we further report that manganese doping creates strongly circularly polarized luminescence, depending on the alignment of the Mn dopant’s magnetic moment. We attribute our observations to spin-dependent exciton dynamics at early times after excitation and show preliminary ultrafast spectroscopy measurements supporting this interpretation. Our results demonstrate magnetic doping as an approach to control spin physics of exciton populations in perovskites. These findings will stimulate research on this highly tuneable material platform with promise for tailored interactions between magnetic moments and excitonic states.