The effect of the existing vertical sidewall on the hydrodynamic characteristics of a π-shaped floating breakwater interacting with water waves in a fluid domain of finite, arbitrary water depth is analyzed. The Scaled Boundary Finite Element Method (SBFEM) is adopted to solve the Laplace governing equation based on the potential flow assumption in a two-dimensional vertical plane. The accuracy and efficiency of the SBFEM-based model are evaluated by comparing the calculated results of the current model with the literature. The presence of a sidewall generally produces more significant responses due to the creation of standing waves and the appearance of the resonance phenomenon, which synchronizes some wavelengths with the distance between the sidewall and the π-shape floating structure. Furthermore, the present model accurately predicts the hydrodynamic behavior, either with sharp corners or a few elements in the solution domain.