This study addresses the gap in understanding the varied effectiveness of group cognitive behavioral therapy (gCBT) delivered by different professionals. This study aims to address this gap by conducting a systematic review of randomized controlled trials (RCTs) that evaluate gCBT and compare it to inactive controls in adults with a clinical diagnosis of depression. A total of 33 RCTs were included for analysis. In the overall analysis, ‘profession of gCBT deliverer’ was not a significant moderator in the meta-regression model (p = 0.57). For people without comorbidity, the overall effect size estimate was −0.69 (95% CI, −1.01. to −0.37, p = 0.03). Among gCBT deliverers, psychologists and nurses/psychiatric nurses demonstrated significant effectiveness, with psychologists showing a large effect size of −0.78 (95% CI, −1.25 to −0.30, p < 0.01) and nurses/psychiatric nurses showing a medium effect size of −0.45 (95% CI, −0.85 to −0.05, p = 0.03). The certainty of evidence for both professionals was moderate. These results have significant implications for the delivery of mental healthcare, as nurses/psychiatric nurses may be more accessible and cost-effective than psychologists in some settings. However, further research is necessary to determine the effectiveness of gCBT delivered by a broader range of healthcare professionals for patients with depression and other comorbidities.