Abstract Background There are increasing concerns about mental health consequences of the COVID-19 pandemic among seafarers. This study aims to assess the effects of the current global health pandemic on life satisfaction and adverse psychological outcomes among seafarers. Methods In this cross-sectional study, 470 multinational seafarers working on board ships of two international shipping companies were assessed. Mental health outcomes were assessed by the general anxiety disorder (GAD-7) questionnaire, post-traumatic stress disorder (PTSD-8) questionnaire, and patient health questionnaire (PHQ-9) depressive severity score. Multivariate logistic regression was used to determine the association of demographic and work-related variables with mental health outcomes. Results Overall, 439 out of 470 invited seafarers with a mean age of 34.5 (SD: 8.05) years participated in this study (participation rate: 93.4%). The prevalence of anxiety, depressive, and post-traumatic stress symptoms was 12.4, 14.1, and 37.3%, respectively. In the multivariate model, the current vessel’s signing duration was directly associated with the odds of depressive and intrusion symptoms. Moreover, the duration of work per week was inversely associated with hyper-vigilance and avoidance. Also, non-officers, compared to officers, experienced significantly lower anxiety and depressive symptoms, hyper-vigilance, and avoidance. Conclusion The present study revealed a high prevalence of mental health problems among seafarers during the COVID-19 pandemic. We recommend that more evidence is generated regarding psychosocial health issues for this vulnerable occupation.