Background Talimogene laherparepvec (T-VEC) is an oncolytic virus approved for the treatment of unresectable, recurrent melanoma. The role of T-VEC after progression on systemic immunotherapy (IO) remains undefined. The goal of this study was to characterize the efficacy of T-VEC after failure of IO in patients with unresectable metastatic melanoma. Methods An international, multi-institutional review of AJCC version 8 stage IIIB-IV melanoma patients treated with T-VEC after failure of IO was performed at six centers from October 2015-December 2020. Primary outcome was in-field response; secondary outcomes included analyses of in-field and overall progression-free survival (PFS) and in-field and overall disease-free survival (DFS) after a complete response. Subset analysis of T-VEC initiation sequentially after or concurrently with IO was performed. Results Of 112 patients, median age at T-VEC initiation was 69 years (range 21–93); 65 (58%) were male. Before T-VEC, 57% patients received one IO regimen, 42% received two or more, with most patients ( n = 74, 66%) receiving T-VEC sequential to IO. Most were stage 3C ( n = 51, 46%) at T-VEC initiation, 29 (26%) received injections to nodal disease. Over median follow-up of 14 months, in-field response at final T-VEC injection was 37% complete (CR), 14% partial (PR). T-VEC initiation sequentially or concurrently did not significantly affect in-field response ( p = 0.26). Median in-field PFS was 15 months (95% confidence interval 4.6-NE). Median overall DFS after CR was 32 months (95% confidence interval 17-NE). Conclusions T-VEC after failure of IO is effective in unresectable, metastatic stage IIIB-IV melanoma. T-VEC initiation sequentially or concurrently did not significantly affect in-field response.