The COVID-19 pandemic has become a public health emergency of international concern, which may affect lifestyle habits and mental health. Based on national health profile assessments, this study investigates perceived changes of lifestyle habits in response to the COVID-19 pandemic and associations between perceived lifestyle changes and mental health in Swedish working adults. Among 5,599 individuals (50% women, 46.3 years), the majority reported no change (sitting 77%, daily physical activity 71%, exercise 69%, diet 87%, alcohol 90%, and smoking 97%) due to the pandemic. Changes were more pronounced during the first wave (April-June) compared to the second (October-December). Women, individuals <60 years, having a university degree, being white-collar workers and having unhealthy lifestyle habits at baseline had higher odds of changing lifestyle habits compared to their counterparts. Negative changes in lifestyle habits as well as more time in mentally passive sitting at home was associated with higher odds of mental ill-health (including health anxiety regarding one’s own and relatives’ health, generalized anxiety and depression symptoms, and concerns regarding employment and economy). The results em-phasize the need to support healthy lifestyle habits to strengthen the resilience in vulnerable groups of individuals to future viral pandemics, and prevent health inequalities in society.