New polynuclear organometallic Platinum Group Metal (PGM) complexes containing di- and tripyridyl ester ligands have been synthesised and characterised using analytical and spectroscopic techniques including H-1, C-13 NMR and infrared spectroscopy. Reaction of these polypyridyl ester ligands with either Ru(p-cymene)Cl-2, Rh(C5Me5)Cl-2 or Ir(C5Me5)Cl-2 dimers yielded the corresponding di- or trinuclear organometallic complexes. The polyaromatic ester ligands act as monodentate donors to each metal centre and this coordination mode was confirmed upon elucidation of the molecular structures for two of the dinuclear complexes. The di- and trinuclear PGM complexes synthesized were evaluated for inhibitory effects on the human protozoal parasites Plasmodium falciparum strain NF54 (chloroquine sensitive), Trichomonas vaginalis strain G3 and the human ovarian cancer cell lines, A2780 (cisplatin-sensitive) and A2780cisR (cisplatin-resistant) cell lines. All of the complexes were observed to have moderate to high antiplasmodial activities and the compounds with the best activities were evaluated for their ability to inhibit formation of synthetic hemozoin in a cell free medium. The in vitro antitumor evaluation of these complexes revealed that the trinuclear pyridyl ester complexes demonstrated moderate activities against the two tumor cell lines and were also less toxic to model non-tumorous cells.