Probing the quantum geometry and topology in condensed matter systems has relied heavily on static electronic transport experiments in magnetic fields. Yet, contact-free optical measurements have rarely been explored. Here, we report the observation of resonant magnetic circular dichroism (MCD) in the infrared range in thin film MnBi_{2}Te_{4} exhibiting a spectral intensity that correlates with the anomalous Hall effect. Both phenomena emerge with a field-driven phase transition from an antiferromagnet to a canted ferromagnet. By theoretically relating the MCD to the anomalous Hall effect via Berry curvature for a metallic state, we show that this transition accompanies an abrupt onset of Berry curvature, signaling a topological phase transition from a topological insulator to a doped Chern insulator. Our density functional theory calculation suggests the MCD signal mainly originates from an optical transition at the Brillouin zone edge, hinting at a potential new source of Berry curvature away from the commonly considered Γ point. Our findings demonstrate a novel experimental approach for detecting Berry curvature through spectroscopy of the interband MCD, generally applicable to magnetic materials.