Background: Outcome-Based Education (OBE) has been increasingly adopted in nursing education to enhance students’ competencies, yet evidence on its global effectiveness remains heterogeneous. This meta-analysis quantitatively evaluates the impact of OBE interventions on clinical competency, knowledge acquisition, critical thinking, and self-efficacy among nursing students. Methods: A systematic search was conducted in PubMed, CINAHL, Scopus, Web of Science, and Embase for studies published between 2010 and 2025. Eighteen studies (4 randomized controlled trials, 14 quasi-experimental) involving 3,820 nursing students were included. Standardized mean differences (SMDs) with 95% confidence intervals (CIs) were calculated using a random-effects model. Subgroup analyses were performed by intervention type (simulation-based, OSCE, traditional OBE). Heterogeneity was assessed with the I² statistic. Results: OBE interventions significantly improved all four outcomes. Clinical competency showed a moderate-to-large effect (SMD = 0.68, 95% CI: 0.45–0.91, I² = 46%), critical thinking was moderately enhanced (SMD = 0.55, 95% CI: 0.32–0.78, I² = 38%), knowledge acquisition improved moderately (SMD = 0.49, 95% CI: 0.28–0.70, I² = 40%), and self-efficacy demonstrated moderate gains (SMD = 0.61, 95% CI: 0.39–0.83, I² = 35%). Subgroup analyses indicated that simulation-based programs yielded the highest effect sizes across outcomes (clinical competency SMD = 0.82; critical thinking SMD = 0.67; knowledge acquisition SMD = 0.55; self-efficacy SMD = 0.66), followed by OSCE and traditional OBE. Conclusions: OBE is an effective educational strategy in nursing programs, enhancing both cognitive and practical competencies. Simulation-based and OSCE-integrated OBE interventions are particularly effective. Findings support the global adoption of competency-focused, outcome-driven curricula to optimize nursing education.