Background: The present research intends to identify the determinants of men’s mental wellbeing during the COVID-19 pandemic. The fear and uncertainty caused by this pandemic and its prolongation have caused a considerable rise in mental health disorders. In a very short time, much research has been conducted examining the main consequences of the COVID-19 pandemic on individuals’ mental health. Some studies pointed out that COVID-19 stressors significantly affect individuals, and some statistics suggest that the pandemic affects men and women differently. However, the literature on the effect of the COVID-19 pandemic on men’s mental health remains limited. This research attempted to fill these gaps in the literature by examining an essential research question about the determinants of men’s mental wellbeing during the COVID-19 pandemic. Methods: This research uses a dataset collected on Eurofound’s Living, Working, and COVID-19 survey, and the full sample consisted of 24,123 European citizens. The sample was split into two main groups: men (N = 3577) and women (N = 8744). This research uses linear regression methodology to investigate the mental wellbeing of male employees. The input method was applied to estimate two regression models, one for men and one for women. Results: Our results revealed that men’s exposure to COVID-19 infection deteriorates their mental wellbeing. Similarly, some organizational factors also determined men’s mental wellbeing, such as working under fixed employment contracts, feelings of doing useful work, and satisfaction with the quality of work. Finally, individual and attitudinal factors contributed to determining the mental wellbeing of male employees, optimism about the future, general health, positive feelings about themselves, and overall life satisfaction. Conclusion: This research deduces that men’s mental wellbeing is determined by factors that are different from those of women employees. In conclusion, this research deduces that men’s good mental wellbeing is determined differently from women employees. Specifically, we identified that exposure to COVID-19, employment contracts at the job, feelings of doing useful work, satisfaction with the quality of work, resilience, age, life satisfaction, general health, optimism about the future, and feeling positive about themselves are the key determinants of men’s health.