A new zwitterionic triamine monomer prepared from tris(2-aminoethyl)amine and 1,3-propane sultone is proposed for the interfacial polymerization with trimesoyl chloride to form thin-film composite membranes for nanofiltration with antifouling properties. The positive effects of the zwitterionic monomer fraction on the surface characteristics of the polyamide layer, fouling resistance, and filtration performance are demonstrated. Increasing the zwitterionic monomers in the selective layer significantly improves the water permeance (two-fold) without affecting the rejection for dyes tested with a molecular weight in the range of 637 and 1673 g/mol. The smoother and more hydrophilic membrane surface of the newly developed membrane provides excellent fouling resistance confirmed by the negligible protein adsorption and permeance drop during the filtration.