Megathrust earthquakes, such as the 2010 Maule and 2011 Tohoku events, have underscored the destructive potential of long-duration ground shaking, which poses unique challenges for structural systems and carries significant societal implications. Traditional seismic design prioritizes peak ground motion parameters, often overlooking the cumulative damage effects associated with prolonged shaking. This study examines the influence of ground motion duration on the seismic performance of reinforced concrete (RC) shear walls using controlled laboratory experiments. Three identical half-scale, flexure-dominated RC shear walls—designed according to pre-2010 Chilean seismic provisions—were subjected to in-plane cyclic loading under distinct displacement protocols. Two specimens experienced nonlinear displacement histories derived from OpenSees time-history analyses: one reflecting long-duration and the other spectrally equivalent short-duration motions. A third specimen served as a control using a conventional cyclic loading protocol. The experimental program details damage progression, failure mechanisms, and performance differences across the specimens. Results reveal that long-duration histories result in more extensive damage, lower displacement capacity, and altered failure modes, aligning with trends observed in recent bridge column studies. These findings advocate for integrating duration-sensitive loading protocols into experimental frameworks and design methodologies to enhance the fidelity of seismic performance evaluations for RC structural systems.