Disrupted sleep has long been associated with physical functioning and disability in chronic pain populations and recent research shows that patterns of sleep and rest can predict physical disability, independent of depression and pain levels in this group. However, it is unknown whether sleep quality may independently predict disability in this way. The aim of the present study was to examine the self-reported relationship between sleep and disability in 155 chronic pain patients attending a pain management service. The sample had an average age of 52.9 years and 69% were female with mean pain duration of 10.5 years. Disrupted sleep and rest patterns and poor sleep quality were positively correlated with depression and pain-related disability. Hierarchical regression analyses showed that sleep quality did not predict pain-related disability when depression and pain severity were taken into consideration. Separate mediation analyses of depression and pain severity revealed that both variables were important partial mediators of the relationship between sleep quality and disability. Depression was found to be a stronger mediator than pain severity. These findings highlight the important role of sleep in chronic pain suffering. However, due to the cross sectional nature of this study, the mediation pathways proposed require testing by further research adopting a prospective design. Ideally, future research should evaluate whether targeted interventions to improve sleep can reduce pain severity, depression and ultimately, pain-related disability.