Caring for a family member with a serious mental illness often has an impact on the quality of life (QoL) of caregivers. This could have negative repercussions on their caring skills and thus affect the care provided to that individual. The aim of this paper is to identify current evidence on QoL factors affecting relatives of individuals suffering from serious mental illness. A systematic review related to the research question was conducted in six databases by two independent reviewers. The QoL factors of relatives include sociodemographic, contextual, psychological, physical, and patient factors. The findings are consistent with the results of previous research. Mental health professionals may support a family with a member diagnosed with a serious mental illness by enhancing their education about QoL factors, which would trigger and promote protective factors so that family members could assess and act on them on an ongoing basis.