Harnessing the cytotoxic ability of CD8+ T-cells has been the predominant focus of modern cancer immunotherapies due to their ability to directly recognise and eliminate tumour cells. These strategies are limited by the emergence of MHC-deficient or IFN-unresponsive tumour cells and the formation of an immunosuppressive tumour microenvironment. The ability of effector CD4+ T-cells to contribute to anti-tumour immunity independently of CD8+ T-cells is increasingly recognised, but the mechanisms of unleashing CD4+ T-cell-mediated anti-tumour immunity remain elusive. Using an adoptive cell therapy model, we show how an indirect CD4+ T-cell-mediated mode of action empowers the destruction of melanomas that escape direct T-cell targeting. Despite being relatively scarce, CD4+ T-cells controlled MHC-deficient and IFN-unresponsive immune-evasive tumours that resist highly abundant CD8+ T-cells. To compare the dynamics of CD4+ and CD8+ T-cells in the tumour microenvironment, we employed two-photon intravital imaging and demonstrate that CD8+ T-cells profoundly infiltrate MHC-competent tumour centres and decelerated in proximity to tumour cells, whereas CD4+ T-cells form local clusters at the tumour invasive margin. In IFN-unresponsive tumours, CD8+ T-cells were not able to infiltrate the tumour centre or form stable interactions with the tumour cells. In contrast to CD8+ T-cells, the migratory behaviour of CD4+ T-cells did not differ in IFN-unresponsive tumours. Instead, CD4+ T-cells preferentially cluster at tumour invasive margins, where they interact with MHC-II+ CD11c+ antigen-presenting cells. Additionally, the CD4+ T-cells synergised with innate immune stimuli to reprogram the tumour-associated inflammatory myeloid network towards IFN-activated antigen-presenting and tumouricidal iNOS-expressing effector phenotypes. IFNg blockade during CD4+ T-cell therapy profoundly abrogated this reprogramming of myeloid cells, by particularly impairing the generation of nitric oxide-secreting monocytes. Nitric oxide inhibition during CD4+ T-cell therapy demonstrated that effector CD4+ T-cells indirectly kill immune-evasive tumours through IFN-dependent activation of myeloid effector cells and the secretion of nitric oxide. Thus, CD4+ T-cells and IFN-activated mononuclear phagocytes initiated inflammatory tumour cell death that acted remotely from the invasive margin. Together, these results warrant the clinical exploitation of CD4+ T-cells and innate immune agonists to complement the direct cytolytic activity of CD8+ T-cells and NK cells to advance cancer immunotherapies.