<p>This study investigates the seismic in-plane cyclic performance of concrete shear walls reinforced with carbon fiber-reinforced polymer (CFRP), with a focus on the influence of key geometric and loading parameters, including horizontal reinforcement ratio, shear–span ratio, axial compression ratio, and specimen size. A validated three-dimensional finite element model (FEM) is developed in ABAQUS to simulate the nonlinear response of CFRP-reinforced shear walls under seismic-type lateral cyclic loading. Parametric analyses show that increasing the horizontal reinforcement ratio significantly improves shear strength, energy dissipation, and deformation capacity while reducing damage concentration. Conversely, higher axial compression ratios induce brittle shear failure and diminish ductility. As the shear–span ratio increases, the pattern of material failure transitions from shear-dominated to flexural-dominated. Nevertheless, the existing ACI 440.11-22 design code neglects the specimen size and shear–span ratio, resulting in inaccurate and non-conservative safety calculations. Subsequent, statistical analysis with 95% confidence intervals indicates that safety margins diminish as wall length extend related to geometric slenderness. Complementary statistical analysis using 95% confidence intervals highlights that safety margins decrease with increasing wall length due to geometric slenderness, with shear–span ratio emerging as the dominant factor affecting SI variability. Despite the consistency of CFRP reinforcement, it yields only marginal enhancements across all scenarios. To address these shortcomings, a new predictive equation is proposed to estimate nominal shear strength as a function of both shear–span ratio and specimen size. The findings provide novel insights into the behavior of CFRP-reinforced shear walls during seismic events and offer valuable, code-compliant resources for enhancing design, increasing earthquake resilience, and ensuring safety.</p>