The Russian invasion of Ukraine on February 24, 2022, had profound impacts on the Ukrainian population and the global economy, environment, and political order. This study examines the psychological well-being of individuals outside Ukraine in the weeks surrounding the outbreak of war. A longitudinal experience-sampling study involving 1,341 participants from 17 European countries (44,894 assessments) tracked well-being levels. The data show a significant decline in well-being on the day of the invasion, with recovery over the following weeks influenced by individual personality traits but not age, gender, social status, or political orientation. Well-being was lower on days when the war was more prominent on social media. The findings highlight the need to consider the psychological implications of the Russo-Ukrainian war alongside its humanitarian, economic, and ecological consequences. The study also suggests that individuals high in the personality trait of Stability recovered more quickly from the initial decline in well-being compared to those low in Stability. Additionally, the salience of the war on social media was negatively associated with daily well-being, indicating a reciprocal relationship between exposure to war-related content and distress. These results provide insights into the psychological impacts of major societal crises and suggest the importance of targeted mental health interventions.The Russian invasion of Ukraine on February 24, 2022, had profound impacts on the Ukrainian population and the global economy, environment, and political order. This study examines the psychological well-being of individuals outside Ukraine in the weeks surrounding the outbreak of war. A longitudinal experience-sampling study involving 1,341 participants from 17 European countries (44,894 assessments) tracked well-being levels. The data show a significant decline in well-being on the day of the invasion, with recovery over the following weeks influenced by individual personality traits but not age, gender, social status, or political orientation. Well-being was lower on days when the war was more prominent on social media. The findings highlight the need to consider the psychological implications of the Russo-Ukrainian war alongside its humanitarian, economic, and ecological consequences. The study also suggests that individuals high in the personality trait of Stability recovered more quickly from the initial decline in well-being compared to those low in Stability. Additionally, the salience of the war on social media was negatively associated with daily well-being, indicating a reciprocal relationship between exposure to war-related content and distress. These results provide insights into the psychological impacts of major societal crises and suggest the importance of targeted mental health interventions.