<p>This paper presents a comprehensive numerical study of the influence of infill wall configurations on the seismic behavior of existing Reinforced Concrete (RC) framed buildings with plan irregularities. Such buildings constitute a large proportion of the global building stock, particularly in Egypt, and many lack adequate seismic detailing. Nonlinear dynamic time-history analyses were performed on two groups of medium- and low-rise L-shaped buildings using SeismoStruct software, employing the double-strut nonlinear cyclic model for infill walls. Five infill wall configurations were developed for each group, ranging from a bare frame structure (BS) to a fully infilled structure (IFS). Three ground motion records with high-, medium-, and low-frequency contents were each scaled to levels ranging from 0.1 to 0.5&#xa0;g for analyzing 150 models. The results show that, with appropriate configuration, infill walls could improve the seismic performance of irregular plan buildings in terms of story drift, rotation, and structural damage. Also, infill walls could provide an effective seismic rehabilitation solution for existing buildings without requiring traditional seismic rehabilitation methods while maintaining their architectural appearance and functional use.</p>