<p>The current study aims to address a critical gap in existing research by focusing on the seismic performance of irregular three-dimensional structures with masonry infill walls. While previous studies have extensively explored infill walls in two-dimensional frames or regular three-dimensional layouts, irregular structures with uneven mass distribution, varying stiffness, and asymmetrical geometry present additional challenges that are not fully captured by traditional methods. To investigate these complexities, the study performs a pushover analysis and examines the results in relation to capacity curves and inter-story drift. Additionally, a fiber-section-based macro-modeling approach was employed to accurately model the infill walls. The findings reveal that incorporating masonry infill walls significantly enhances both lateral stiffness and base shear capacity, leading to improved overall stability during seismic events. The analysis shows steeper capacity curves with infill walls, indicating increased stiffness and reduced maximum displacements, though this can sometimes reduce ductility, which is essential for accommodating large deformations without structural failure. Structures with O and U shapes demonstrate an effective balance between stiffness and ductility, resulting in superior seismic performance. Overall, infill walls are crucial for distributing seismic forces more effectively and minimizing the risk of structural failure, even in irregular designs. Their inclusion in structural modeling is vital for achieving accurate performance predictions and ensuring robust seismic resistance.</p>