Background Changes in dietary behaviors that occurred at the beginning of the COVID-19 outbreak and in particular during the first national lockdowns have been extensively studied across countries. Beyond the understanding of contextual changes in diets due to a temporary lockdown, it is of interest to study longer-term consequences of the COVID-19 outbreak as sustained changes in diets may have both an impact on population health and the environment. Objectives This study aimed to examine both short- (after 1 month) and mid-term (after 1 year) impacts of the COVID-19 outbreak on the nutritional quality and environmental impact of diets, and as a secondary objective on food choice motives. Methods We collected dietary data [food frequency questionnaire (FFQ)] and the importance of nine food choice motives through online questionnaires before, during, and after 1 year of the first lockdown for 524 French participants. Adherence to the French dietary recommendations was estimated using the simplified PNNS-GS2, which scores from −17 to 11.5. Environmental impact of diets was assessed by calculating greenhouse gas emissions in CO2eq/2,000 kcal. Results We showed a short-term decrease in nutritional quality (−0.26 points on sPNNS-GS2, p = 0.017) and environmental impact (−0.17 kg CO2eq/2,000 kcal, p = 0.004) but this decrease was only temporary, and nutritional quality (−0.01 points on sPNNS-GS2, p = 0.974) and environmental impact (−0.04 kg CO2eq/2,000 kcal, p = 0.472) were not different from their initial values 1 year later. Some of the food choice motives followed the trend of a short-term increase and a mid-term stability (health, natural content, ethical concern, and weight control). On the contrary, we showed both short- and mid-term decreases in convenience, familiarity, and price motives. Conclusion Changes in diets and motives observed during the first lockdown were mostly temporary. However, we highlighted a sustained decrease in the importance of perceived constraints due to food shopping and food preparation which may suggest a trend toward a more positive perception of food-related activities.