RATIONALE: The importance of the adaptative T cell response in the control and resolution of viral infection has been well-established. However, the nature of T cell-mediated viral control mechanisms in life-threatening stages of COVID-19 has yet to be determined. OBJECTIVE: The aim of the present study was to determine the function and phenotype of T cell populations associated with survival or death of COVID-19 patients under intensive care as a result of phenotypic and functional profiling by mass cytometry. FINDINGS: Increased frequencies of circulating, polyfunctional, CD4+CXCR5+HLA-DR+ stem cell memory T cells (TSCM) and decreased proportions of Granzyme-B and Perforin-expressing effector memory T cells (TEM) were detected in recovered and deceased patients, respectively. The higher abundance of polyfunctional CD8+PD-L1+CXCR3+ T effector cells, CXCR5+HLA-DR+ TSCM, as well as anti-nucleocapsid (NC) cytokine-producing T cells permitted to differentiate between recovered and deceased patients. The results from a principal component analysis showed an imbalance in the T cell compartment allowed for the separation of recovered and deceased patients. The paucity of circulating CD8+PD-L1+CXCR3+ Teff-cells and NC-specific CD8+ T-cells accurately forecasts fatal disease outcome. CONCLUSION: This study provides insight into the nature of the T cell populations involved in the control of COVID-19 and therefor might impact T cell-based vaccine designs for this infectious disease.