Introduction: Electrical cardioversion is used commonly in patients with atrial fibrillation (AF). However, success rates vary and practical guidance is limited. Methods: We searched CENTRAL, Medline and EMBASE from inception to present and the grey literature. We included randomized controlled trials (RCTs) comparing any two interventions. Outcomes were initial and cumulative cardioversion success. We pooled data using random effects models. Results: From 13481 citations, we included 52 RCTs. Biphasic as compared to monophasic waveforms resulted in a higher rate of cardioversion for initial (18 studies, risk ratio [RR] 1.45, 95% confidence interval [CI] 1.10-1.90, I 2 =89%) and cumulative success (21 studies, RR 1.07, 95% CI 1.02-1.13, I 2 =75%). Fixed, maximum-energy shocks as compared to low-dose escalating energy protocols had a higher likelihood of initial (4 studies, RR 1.62, 95% CI 1.33-1.98, I 2 =72%) but not cumulative success (3 studies, RR 1.13, 95% CI 0.97-1.32, I 2 =86%). Initial or cumulative cardioversion success did not differ significantly for several other interventions. This included: antero-apical/lateral vs. anteroposterior positioned pads (initial: 10 studies, RR 1.06, 95% CI 0.89-1.27; cumulative: 13 studies, RR 0.99, 95% CI 0.95-1.04); rectilinear/pulsed biphasic vs. biphasic truncated exponential waveform (initial: 3 studies, RR 1.07, 95% CI 0.76-1.50; cumulative: 3 studies, RR 0.95, 95% CI 0.80-1.12); cathodal vs. anodal configuration (cumulative: 2 studies, RR 1.03, 95% CI 0.97-1.09); magnesium pre-treatment vs. none (initial: 2 studies, RR 1.36, 95% CI 0.82-2.24; cumulative: 2 studies, RR 1.05, 95% CI 0.96-1.14); and patches vs. manual pressure/paddles (initial: 2 studies, RR 1.04, 95% CI 0.26-4.12; cumulative: 2 studies, RR 0.87, 95% CI 0.61-1.25). Conclusions: Biphasic shock waveforms and high-energy shocks increase the efficacy of cardioversion of AF. Other interventions, including pad placement, biphasic waveform properties, electrode polarity, electrolyte pre-treatment, and manual pressure require further study.