The cytotoxicity of two tricarbonyl Mn(I) complexes of the general formula fac-[MnBr(CO)3L] (L = quinoline-2-carboxaldehyde (A) and 8-amino quinoline (B)) towards triple negative breast cancer (MDA-MB-231) was reported. Complexes A and B released CO when exposed to 468 nm light. Compound B has a dose-dependent cytotoxicity, with half maximal inhibitory concentration values of 19.62 μM and 11.43 μM before and after illumination, respectively. Co-treatment of MDA-MB-231 with paclitaxel (30 nM) and complex B (10 μM) resulted in a 50% reduction in cell viability.