Low back pain (LBP) is a leading cause of work disability. While absent from work, workers with LBP may receive income support from a system such as workers' compensation or social security. This study examines how and in what contexts income support systems impact the healthcare quality for people with work disability and LBP and their functional capacity. We performed a realist review. Five initial theories about the relationship between income support systems and outcomes were developed, tested, and refined by acquiring and synthesising academic literature from purposive and iterative electronic database searching. This process was supplemented with gray literature searches for policy documents and semistructured interviews with experts in income support, health care, and LBP. Income support systems influence healthcare quality through funding restrictions, healthcare provider administrative burden, and allowing employers to select providers. They also influence worker functional capacity through the level of participation and financial incentives for employers, measures to prove the validity of the worker's LBP, and certain administrative procedures. These mechanisms are often exclusively context-dependent, and generate differing and unintended outcomes depending on features of the healthcare and income support system, as well as other contextual factors such as socioeconomic status and labour force composition. Research and policy design should consider how income support systems may indirectly influence workers with LBP through the workplace.