Postictal agitation (PIA) is an adverse effect of electroconvulsive therapy (ECT) and is known to predict other side effects of ECT, but inconsistencies in the literature remain regarding PIA prognostic factors and incidence. Therefore, a systematic review and meta-analysis were conducted (1) to identify prognostic factors for PIA following ECT and (2) to elucidate the diverse incidences of PIA following ECT based on demographic and clinical characteristics. Specifically, electronic databases were searched for retrospective observational studies and randomized controlled trials (RCTs) that objectively reported PIA incidence. Additional inclusion criteria encompassed studies involving patients 18 years or older and allowed for the extraction of PIA prognostic factors. This resulted in the inclusion of 21 articles with 66,047 patients in total. A total of 35 prognostic factors were identified for PIA after ECT, consisting of 8 anesthesia-related, 19 patient-related, and 8 ECT-related prognostic factors. A meta-analysis was conducted for 7 prognostic factors. None of the prognostic factors demonstrated a significant effect on reducing or increasing PIA incidence. Mean PIA was 13.9% (18.0% adjusted) at the patient level and 12.4% (16.5% adjusted) at the session level. Overall risk of bias was generally moderate to low, except in the outcome measurement domain, where 43% of the studies had a high risk of bias. Although none of the prognostic factors in meta-analysis were significant, several other prognostic factors consistently indicated increased or decreased risk, providing direction for future research. A scarcity of (high-quality) data emphasizes the need for additional research on this topic to be conducted.