Background: The present meta-analysis evaluates the efficacy of psychological interventions for grief in bereaved adults and explores the possible moderating influence of various study characteristics. Methods: A systematic literature search was conducted by two reviewers who independently searched electronic databases, reviewed and selected eligible studies, and evaluated their methodological quality. Results: A total of 31 randomized controlled trials (RCTs) were included in the meta-analysis. Statistically significant pooled effects of psychological intervention on grief symptoms were found for both post-intervention (Hedges's g = 0.41, p > .001, K = 31) and follow-up (g = 0.45, p > .001, K = 18). While generally robust, the effect was smaller at post-intervention when adjusting for possible publication bias (g = 0.31). Compared with the remaining studies, larger post-intervention effect sizes were found for studies with (1) individually delivered interventions (Beta = 0.49, p < .001), (2) the ICG-(R)/PG-13 questionnaire as the grief instrument (Beta = 0.46, p < .001), (3) participants who were ≥6 months post-loss (Beta = 0.58, p < .001), (4) participants included based on high baseline symptom levels (Beta = 0.40, p = .002) and (5) higher study quality (Beta = 0.06, p = .013). Limitations: The included studies were methodologically heterogeneous and their methodological quality varied considerably. Moreover, there were some indications of publication bias. Conclusions: Given the recent introduction of Prolonged Grief Disorder in the ICD-11, the results of the present meta-analysis are timely and of clinical relevance. Based on our results, psychological intervention appears efficacious for alleviating grief symptoms in bereaved adults, with several study characteristics as possible moderators of the effect. The interpretability of the results, however, is challenged by some limitations of the available research, including possible publication bias.