The synthesis and characterization of Ru(II) terpyridine complexes derived from 4′-functionalized 2,2′:6′,2″-terpyridine ligands by a multi step procedure have been described. The complexes are redox-active, showing both metal-centred (oxidation) and ligand-centred (reduction) processes. The antibacterial and antifungal activity of the synthesized ruthenium(II) complexes [Ru(attpy)₂](PF₆)₂ (attpy = 4′-(4-acryloyloxymethylphenyl)-2,2′:6′,2″-terpyridine); [Ru(mttpy)₂](PF₆)₂ (mttpy = 4′-(4-methacryloyloxymethylphenyl)-2,2′:6′,2″- terpyridine); [Ru(mttpy)(MeOPhttpy)](PF₆)₂ (MeOPhttpy = 4′-(4-methoxyphenyl)-2,2′:6′,2″-terpyridine); and [Ru(mttpy)(ttpy)](PF₆)₂ (ttpy = 4′-(4-methylphenyl)-2,2′:6′,2″-terpyridine) were tested against four human pathogens (Proteus vulgaris, Proteus mirabilis, Pseudomonas aeruginosa and Escherichia coli) and five plant pathogens (Curvularia lunata, Fusarium oxysporum, Fusarium udum, Macrophomina phaseolina and Rhizoctonia solani) by the well diffusion method and MIC values of the complexes are reported. A biological study of the complexes indicated that the complexes [Ru(mttpy)₂](PF₆)₂ and [Ru(mttpy)(MeOPhttpy)](PF₆)₂ exhibit very good activity against most of the test pathogens and their activity is better than those of some of the commercially available antibiotics like tetracycline and the fungicide carbendazim.