We report a strong enhancement of the magneto-optical Kerr effect (MOKE) in thin films of the non-collinear antiferromagnet Mn3Sn achieved through dielectric-layer engineering. While Mn3Sn exhibits a relatively strong Kerr response compared to most antiferromagnets, further enhancement is important in thin-film geometries to improve optical contrast and sensitivity for probing antiferromagnetic domains and switching dynamics. We employ optical modeling based on the transfer-matrix formalism, incorporating experimentally determined refractive indices and the Voigt parameter of Mn3Sn. The model predicts that interference effects introduced by a dielectric overlayer, involving the controlled amplitude and phase of reflected light, can strongly enhance the Kerr signal, with the enhancement scaling with the dielectric refractive index. Guided by these calculations, we fabricate m-plane-oriented Mn3Sn thin films capped with MgO overlayers of varying thickness. Polar MOKE measurements demonstrate a Kerr rotation enhancement by a factor of 3.84 ± 0.09 under optimal interference conditions, in excellent agreement with the modeling. This work establishes a practical interference-based design framework for enhancing magneto-optical readout of antiferromagnetic order.