Social support is an important extra-therapeutic context of depression treatment, yet no overall estimate is available on how depression treatment affects social support or the size of such an effect. We conducted a meta-analysis of clinical trials of psychotherapy for depression that reported results for social support at post-treatment. A total of 1,579 adults with depression from 11 trials comparing psychotherapy to care-as-usual or waiting list were included. The majority of these studies assessed the participants’ perceptions of social support. Specifically, three studies targeted women with postpartum depression, and four studies targeted individuals with chronic disease. In all these studies, psychotherapy had a small to moderate, yet consistent effect on social support compared to care-as-usual or waiting list at post-treatment (g = 0.38; 95 % CI 0.29–0.48) and at 3–6 month follow-up (g = 0.38; 95 % CI 0.14–0.63). Little evidence of heterogeneity was found across studies, and the results were consistent in several sensitivity analyses. No significant publication bias was detected (Egger’s test p > 0.1). The result of meta-regression showed that improvement in depression symptoms was associated with improvement in social support, but this was not statistically significant.