While the majority of ionomers for proton exchange membrane fuel cells are prepared via solution polymerization and subsequent casting into a membrane, the employment of surface-initiated polymerization of ionomer films from the electrode surface offers the advantages of uniform coverage throughout complex electrode architectures and precise tailoring of the catalyst/ionomer interface. We have developed a new type of ionomer based on surface-initiated ring-opening metathesis polymerization of polynorbornene and facile sulfonation with sulfuric acid. The feasibility of our approach is demonstrated via the growth and sulfonation of a ~90 nm polynorbornene film on a two dimensional gold surface. Sulfonation of the film lowers the resistance of the film against proton transfer by 5 orders of magnitude. Polymerization of norbornene monomers modified with fluorocarbon and hydrocarbon side chains and subsequent sulfonation of the thin film provides an approach for further tailoring of the ionomer to generate a driving force towards film self organization.