BACKGROUND: Coronavirus disease 2019 (COVID-19) can affect multiple organs, especially the lungs, which may lead to intensive care unit (ICU) admission in the case of acute respiratory distress syndrome (ARDS). Other unfavorable outcomes can occur such as need for orotracheal intubation (OTI) and/or extracorporeal membrane oxygenation (ECMO) and even death. We took advantage of national surveillance data from ICU admissions managed by Santé publique France to investigate the factors associated with mortality, severe ARDS, ICU-free days as well as need for invasive ventilatory support in mainland France between February 2020 and June 2021. METHODS: This nationwide cohort study analyzed critically ill COVID-19 patients admitted to ICU. We used Fine and Gray's model and linear and logistic regressions to assess the factors associated with different outcomes. The main variable of interest was the first three periods of the pandemic: period 1 (February to July 2020), period 2 (August to December 2020) and period 3 (January to June 2021). We stratified all analyses according to predefined age groups: <45, 45-64 and ≥65 years. RESULTS: The 15,423 included patients were mainly men (70%). Mean age was 64.1 ± 13.0 years. Mortality remained high throughout all three pandemic periods. The third pandemic period was associated with a higher risk of severe ARDS in patients aged ≥65 years as well as more ICU-free days and less use of invasive respiratory support regardless of age. Obesity was associated with a lower risk of death in patients aged ≥45 and a higher risk of severe ARDS and requiring invasive respiratory support in patients aged ≥65. Male sex was associated with a higher risk of death regardless of age, a higher risk of severe ARDS in patients aged ≥45 as well as fewer ICU-free days and a higher risk of using invasive respiratory support in patients aged ≥65. CONCLUSION: Prognosis did not significantly improve over time for COVID-19 patients admitted to ICU, however our findings highlight obesity and male sex as key factors in most severe COVID-19 cases, particularly in the elderly. This study also showed a reduction in the use of invasive respiratory support, irrespective of patient severity.