Importance Most adults living with major depressive disorder (MDD) fail to achieve remission with conventional antidepressants. The US Food and Drug Administration (FDA) has approved 5 atypical antipsychotics in MDD on the basis of their substantial evidence of efficacy and safety. Objective To compare the efficacy and acceptability of FDA-approved atypical antipsychotics for the adjunctive treatment of MDD in order to provide decision support to practitioners and persons with lived experience. Data Sources A systematic search was conducted using PubMed/MEDLINE, PsycINFO, the Cochrane Library, and Embase from database inception through July 15, 2025. Study Selection Six independent raters screened publications for eligibility. Inclusion criteria were atypical antipsychotics that are FDA approved in the adjunctive treatment of MDD. Data Extraction and Synthesis Two independent raters obtained data and examined risk of bias in accordance with the Cochrane criteria. Effect sizes were synthesized using random-effects models. Data were analyzed from August to September 2025. Main Outcomes and Measures The primary outcomes were efficacy (ie, ≥50% reduction from baseline in the total Montgomery-Åsberg Depression Rating Scale [MADRS] score) and acceptability (ie, all-cause discontinuation). Results A total of 22 short-term studies comprising 10 962 participants (aripiprazole: n = 1297; brexpiprazole: n = 1973; cariprazine: n = 1894; lumateperone: n = 483; quetiapine extended release [XR]: n = 719; and placebo: n = 4596) were included for analysis. Lumateperone had the highest effect size for efficacy (risk ratio [RR], 1.72; 95% credible interval [CrI], 1.40-2.15), followed by aripiprazole (RR, 1.53; 95% CrI, 1.32-1.77), brexpiprazole (RR, 1.38; 95% CrI, 1.18-1.65), cariprazine (RR, 1.20; 95% CrI, 1.07-1.36), and quetiapine XR (RR, 1.15; 95% CrI, 0.96-1.35). A hierarchy of acceptability was observed, with aripiprazole exhibiting the highest acceptability (RR, 1.16; 95% CrI, 0.89-1.50), followed by cariprazine (RR, 1.44; 95% CrI, 1.15-1.82), brexpiprazole (RR, 1.47; 95% CrI, 1.18-1.85), quetiapine XR (RR, 1.56; 95% CrI, 1.14-2.12), and lumateperone (RR, 2.30; 95% CrI, 1.45-3.84). Secondary outcomes (eg, symptomatic remission) and exploratory outcomes (eg, clinically significant weight gain) accorded with the coprimary outcomes. Conclusions and Relevance This systematic review and meta-analysis indicates that differences exist between adjunctive atypical antipsychotics in the treatment of MDD with respect to overall efficacy and acceptability, which should be simultaneously considered. The absence of adequate and well-controlled studies documenting maintenance efficacy of adjunctive atypical antipsychotics in MDD remains a knowledge gap.