SARS-CoV-2 causes a spectrum of COVID-19 disease, the immunological basis of which remains ill-defined . We analysed 85 SARS-CoV-2-infected individuals at acute and/or convalescent timepoints, up to 102 days post-symptom onset, quantifying 184 immunological parameters . Acute COVID-19 presented with high levels of IL-6, IL-18 and IL-10 and broad activation marked by upregulation of CD38 on innate and adaptive lymphocytes and myeloid cells . Importantly, activated CXCR3+cTFH1 cells in acute COVID-19 significantly correlate with and predict antibody levels and their avidity at convalescence as well as acute neutralisation activity . Strikingly, intensive care unit (ICU) patients with severe COVID-19 display higher levels of soluble IL-6, IL-6R, IL-18, and hyperactivation of innate, adaptive and myeloid compartments than patients with moderate disease . Our analyses provide a comprehensive map of longitudinal immunological responses in COVID-19 patients and integrate key cellular pathways of complex immune networks underpinning severe COVID-19, providing important insights into potential biomarkers and immunotherapies.