<p>This paper investigates the in-plane response of unreinforced masonry walls with particular emphasis on the effects of constraint conditions using two distinct methodologies: numerical and analytical. The numerical approach entailed the development of a three-dimensional finite element model of the wall, adhering to a heterogeneous modelling strategy, which was subsequently validated against published experimental study. A detailed parametric study was undertaken to investigate how change in constraint conditions alters the influence of various parameters like pre-compression, Height to Length (H/L) ratio of the wall and H/L ratio of the bricks on the in-plane behaviour of masonry walls. The second approach implemented analytical design code formulations (Eurocode) in conjunction with Monte Carlo Simulations to determine the dominant failure mechanism, in-plane force capacity, stiffness and drift limits, while accounting for material uncertainty intrinsic to masonry. These stochastic simulations facilitated a parametric investigation, akin to that conducted using numerical modelling, thereby enabling a comprehensive comparative assessment between the findings obtained from both methodologies. The findings from numerical modelling demonstrated the interrelation of various factors assessed during parametric investigation, which influenced the structural response of masonry walls under in-plane loading, thus underscoring the necessity of adopting a heterogenous modelling approach for numerical analysis of masonry walls. Comparative analysis showed that analytical models significantly overestimated the in-plane force capacity, stiffness and drift limits as compared to numerical models, suggesting a need for revision and improvement in design codes to ensure safe and robust structural design.</p>