A new class of ionomer was developed through sulfonation of the metallocene-based poly(ethylene-octene) elastomer, followed by its neutralization with zinc acetate. Ionomeric products were characterized through Fourier transform infrared (FT-IR) spectroscopy, small angle X-ray scattering (SAXS), and transmission electron microscopy (TEM) studies. The effect of pendant chain length on the ionomeric modification was also studied through the variation of the comonomer. The impact of these ionomeric modifications on various physico-mechanical properties was thoroughly investigated by using differential scanning calorimetry, mechanical, dynamic mechanical, and thermogravimetric analysis. The resultant properties were correlated with structures of the modified elastomers. Ionomerisation of the base elastomers causes a significant improvement in the stress-strain, as well as the thermal properties compared to the corresponding pristine elastomer.