The primary aim of this systematic review and meta-analysis was to assess the proportion of patients with Treatment Resistant Schizophrenia (TRS) that respond to ECT augmentation of clozapine (C + ECT). We searched major electronic databases from 1980 to July 2015. We conducted a random effects meta-analysis reporting the proportion of responders to C + ECT in RCTs and open-label trials. Five clinical trials met our eligibility criteria, allowing us to pool data from 71 people with TRS who underwent C+ ECT across 4 open label trials (n = 32) and 1 RCT (n = 39). The overall pooled proportion of response to C + ECT was 54%, (95% CI: 21.8–83.6%) with some heterogeneity evident (I2 = 69%). With data from retrospective chart reviews, case series and case reports, 192 people treated with C + ECT were included. All studies together demonstrated an overall response to C + ECT of 66% (95% CI: 57.5–74.3%) (83 out of 126 patients responded to C + ECT). The mean number of ECT treatments used to augment clozapine was 11.3. 32% of cases (20 out of 62 patients) with follow up data (range of follow up: 3–468 weeks) relapsed following cessation of ECT. Adverse events were reported in 14% of identified cases (24 out of 166 patients). There is a paucity of controlled studies in the literature, with only one single blinded randomised controlled study located, and the predominance of open label trials used in the meta-analysis is a limitation. The data suggests that ECT may be an effective and safe clozapine augmentation strategy in TRS. A higher number of ECT treatments may be required than is standard for other clinical indications. Further research is needed before ECT can be included in standard TRS treatment algorithms.