Following SARS-CoV-2 infection, some individuals develop Long-COVID-syndrome lasting for more than 3 months. We analyzed blood samples from patients with Long-COVID, controls without persistent symptoms following SARS-CoV-2-infection and non-infected donors without a history of infection. Long-COVID patients showed clear signs of T cell hyper-activation predominantly in the CD8+ T cell subset with a 4-fold higher expression of CD25 and 2-fold more effector-memory T cells. Following polyclonal T cell stimulation, we found a 2-fold stronger upregulation of CD25 and a 7-fold higher release of IL-3 in Long-COVID. Intracellular staining revealed 5-fold more IL-3-expressing CD8+ T cells in Long-COVID, while GM-CSF, IFN-γ and IL-2 were much less upregulated. These changes correlated with the severity of Long-COVID and persisted for up to 18 months after infection. Our data reveal a pronounced and long-lasting CD8+ T cell hyper-activation and hyper-reactivity in Long-COVID and speak for a trial of T cell-immunosuppression in patients with Long-COVID.