We report a nearly fourfold enhancement of the magneto-optical Kerr effect (MOKE) in thin films of the non-collinear antiferromagnet Mn${}_3$Sn achieved through dielectric-layer engineering. While Mn${}_3$Sn exhibits a relatively strong Kerr response, further enhancement is crucial in thin-film geometries to improve optical contrast when probing antiferromagnetic domains and switching dynamics. We employ optical modeling based on the transfer-matrix formalism, incorporating experimentally determined refractive indices of Mn${}_3$Sn and fitting the complex Voigt parameter $Q$. The model predicts that the Kerr signal enhancement increases with the refractive index of the dielectric. Experimentally, we fabricate $m$-plane-oriented Mn${}_3$Sn thin films capped with MgO overlayers of varying thickness. Polar MOKE measurements reveal an enhancement of the Kerr rotation by a factor of $3.84\pm 0.09$ under optimal interference conditions, in excellent agreement with the modeling. Furthermore, the fitted Voigt parameter serves as a practical descriptor of magneto-optical coupling strength, and these results establish a general interference-based design framework for enhancing magneto-optical readout in unconventional magnetic materials.