Poly(methyl methacrylate) (PMMA)-based dielectric materials are of prime interest for many electronic and power devices. However, the low dielectric constant and hydrophobic nature of PMMA limit its success in many applications. This work presents an environmentally friendly approach to surface-functionalize PMMA, exploring the use of dopamine (DOPA), to develop multifunctional polymers with enhanced dielectric properties. The reaction of dopamine with plasma pre-activated PMMA was carried out in an aqueous medium without using any toxic chemicals. The functionalized PMMA films exhibited enhanced dielectric properties compared to pristine PMMA films. As an example, below 100 Hz, the dielectric constant of functionalized PMMA films increased by 70% compared to pristine PMMA films. Interestingly, functionalization changed the storage modulus and the Tg of PMMA. The enhanced dielectric properties of the functionalized PMMA films may originate from the excellent intrinsic properties of DOPA, which was effectively functionalized on the surface of PMMA.