The complexation equilibria of L-norleucine and gallic acid were studied in aqueous solutions at 25.00 °C and ionic strength 0.15 mol⋅dm−3 (NaNO3), by means of potentiometry and spectrophotometry. The ferric (FeIII), chromium (CrIII), and cupric (CuII) complexing abilities of L-norleucine and gallic acid, along with their overall stability constants, were obtained with the HYPERQUAD 2008 program from the potentiometric data. The concentration distributions of the various complex species in solution were evaluated and discussed. UV–visible spectroscopic measurements were carried out to give qualitative information about the composition of the complexes formed in these solutions. The cytotoxic activities of the binary and ternary metal complexes of L-norleucine and gallic acid were tested and evaluated against HEp-2 (human laryngeal carcinoma), Daoy (human medulloblastoma), MCF-7 (human breast adenocarcinoma), and WiDr (human colon adenocarcinoma) tumor cell lines. Also, their antioxidant activities were examined by free radical scavenging assay.