This study explores how sleep quality influences work engagement and whether mental and physical health help explain that relationship. Survey data from employees across a range of industries showed that people who reported better sleep were more likely to feel energised, dedicated, and absorbed in their work. The findings suggest this relationship is largely explained by mental health rather than physical health. Employees with better sleep tended to report better mental wellbeing, which in turn was linked to higher work engagement. The study highlights sleep as an often-overlooked factor that can influence how people experience and perform at work.