The first mixed ligand Mn (II) and Cd (II) complexes containing 4‐methoxy‐pyridine‐2‐carboxylic acid (4‐mpic) and 4,4′‐dimethyl‐2,2′‐bipyridine (dmbpy) were synthesized in this study. The geometric structures of [Mn(4‐mpic)2(dmbpy)] (complex 1) and [Cd(4‐mpic)2(dmbpy)] (complex 2) were determined by single crystal X‐Ray diffraction method. FT‐IR and UV–Vis spectra were also recorded to investigate vibrational and electronic properties of complexes 1 and 2. Density functional theory (DFT) calculations were also carried out to provide a deep understanding in geometric, spectroscopic, electronic and nonlinear optical (NLO) properties of complexes 1 and 2. The first‐order hyperpolarizibility (β) parameter calculated as 332.9736 × 10−30 esu demonstrated that complex 1 is an extremely promising candidate to NLO materials. Natural bond orbital (NBO) analysis not only verified the distorted octahedral geometries of central metal ions, but also found out the high‐energy interactions responsible for biological activities for complexes 1 and 2. Anti‐cancer activities of complexes 1 and 2 were tested on human breast carcinoma cell line MCF‐7 (ER and PR positive, HER2 negative) and the triple negative breast carcinoma cell line MDA‐MB 231 (ER, PR and HER2 negative). Dose–response relationship derived from MTT assays indicates that complexes 1 and 2 are showing concentration‐dependent effects, which could suggest a potential use for these drug combinations in cancer cell lines.