While socioeconomic disparities are among the most fundamental causes of health disparities, socioeconomic status (SES) does not impact health directly. One of the potential mediating factors that link SES and health is health literacy (HL). Yet although HL can be considered a modifiable risk factor of socioeconomic disparities in health, the relationship between SES, HL and health disparities is not well understood. This study reviewed the evidence regarding the mediating role of HL in the relationship between socioeconomic and health disparities. Medline, Cinahl, Embase, PsychInfo, Eric, Web of Science, Google, Google Scholar, Mednar, Doaj and Worldcat were used to retrieve studies that specifically addressed socioeconomic and socio-demographic factors related to low HL levels, as well as the mediating role of HL in the relationship between SES and disparities in health outcomes. Selected studies were assessed for methodological quality. Sixteen published studies were retained for inclusion and content analyzed using the constant comparison method. The review indicates that disadvantaged social and socioeconomic conditions contribute to low HL levels, whereby low SES, and particularly educational attainment, is the most important determinant of HL, and that HL mediates the relationship between SES and health status, quality of life, specific health-related outcomes, health behaviors and use of preventive services. HL can be considered as a modifiable risk factor of socioeconomic disparities in health. Enhancing the level of HL in the population or making health services more accessible to people with low HL may be a means to reach a greater equity in health.