Electroconvulsive therapy (ECT) is an effective intervention for severe unipolar and bipolar depression, yet its drawbacks often lead to its underutilization. Accurate prediction of ECT outcomes is crucial for optimizing patient care and increasing remission rates. This study synthesized existing evidence on the relationship between baseline inflammatory markers and ECT outcomes. Additionally, we explored whether changes in these markers during ECT correlated with symptom improvement. A correlation meta-analysis was conducted according to the PRISMA statement, including a total of fourteen studies (n = 556 patients). The analyses revealed that higher baseline CRP and IL-6 levels were significantly associated with greater depressive symptom reduction post-ECT. Additionally, our findings suggested that increases in kynurenine metabolites and IL-8 during treatment correlated with improved depressive symptoms, offering insights into the mechanistic aspects of depression and ECT. In conclusion, peripheral inflammation in depression, as measured by CRP and IL-6, is associated with better ECT outcomes and may guide treatment stratification. Further research on a broader range of cytokines and kynurenine metabolites is needed to confirm these findings.