The prevalence of complex health and social needs in primary care patients is growing. Furthermore, recent research suggests that the impact of psychosocial distress on the significantly poorer health outcomes in this population may have been underestimated. The potential of social work in primary care settings has been extensively discussed in both health and social work literature and there is evidence that social work interventions in other settings are particularly effective in addressing psychosocial needs. However, the evidence base for specific improved health outcomes related to primary care social work is minimal. This review aimed to identify and synthesise the available evidence on the health benefits of social work interventions in primary care settings. Nine electronic databases were searched from 1990 to 2015 and seven primary research studies were retrieved. Due to the heterogeneity of studies, a narrative synthesis was conducted. Although there is no definitive evidence for effectiveness, results suggest a promising role for primary care social work interventions in improving health outcomes. These include subjective health measures and self-management of long-term conditions, reducing psychosocial morbidity and barriers to treatment and health maintenance. Although few rigorous study designs were found, the contextual detail and clinical settings of studies provide evidence of the practice applicability of social work intervention. Emerging policy on the integration of health and social care may provide an opportunity to develop this model of care.