This study uses an analytical model and nonlinear static analysis to evaluate the seismic performance of reinforced concrete (RC) frames with brick masonry infill. The analytical model replaces the masonry infill with a diagonal strut, representing the distributed compression between the frame and masonry infill interface. The lateral strength of infilled frames is expressed as a function of the equivalent strut width of the infill. Four structure models, including one RC bare frame and three brick-infilled frames, are analyzed using this analytical model. The analytical results, presented as the relationship between lateral force and drift in a bilinear curve, demonstrate the significant contribution of brick infill to the lateral strength and ductility of the structure. The seismic performance of infilled frame structures is validated through nonlinear static analysis, and remarkably similar results are obtained from both analytical and nonlinear static analyses. In conclusion, the diagonal strut model and nonlinear static analysis effectively estimate the seismic performance of infilled RC frames. The findings have implications for the field of structural engineering, highlighting the importance of brick masonry infill in enhancing the seismic resilience of RC structures.