Catalyzes the formation of the NeuAc-alpha-2,3-Gal-beta-1,4- GlcNAc-, NeuAc-alpha-2,3-Gal-beta-1,3-GlcNAc- and NeuAc-alpha-2,3-Gal- beta-1,3-GalNAc- sequences found in terminal carbohydrate groups of glycoproteins and glycolipids. The highest activity is toward Gal-beta- 1,3-GlcNAc and the lowest toward Gal-beta-1,3-GalNAc. . This is the function of ENSG00000126091 (ST3GAL3, ST3 beta-galactoside alpha-2,3-sialyltransferase 3).