The study compared the effectiveness of different beta-blockers in preventing arrhythmic events in 5692 patients with long QT syndrome (LQTS) from 10 cohort studies using a random-effects network meta-analysis. In patients with LQT1, nadolol was superior to propranolol (RR = 0.59, 95% CI: 0.39–0.90) and had the highest probability of optimal treatment (SUCRA = 0.92), although dose–response trends for all drugs were nonsignificant (all p > 0.05). For LQT2, no beta-blocker showed significant superiority, but nadolol (SUCRA = 0.78) and propranolol (SUCRA = 0.65) were the highest; nadolol had a significant dose-response relationship (slope = -0.01763, p = 0.010). For LQT3, no treatment was significantly different from atenolol, although SUCRA favored nadolol (0.85) and propranolol (0.75), with a significant dose-response for nadolol (slope = -0.02136, p = 0.023). Placebo showed an unexpected risk reduction versus atenolol (RR = 0.63, 95% CI: 0.42–0.93, p = 0.02), possibly due to baseline imbalance. Consistency (p > 0.38) and sensitivity analyzes confirmed the robustness of the findings.