Sexual minority (SM) individuals are more likely to experience mental health concerns than heterosexual individuals. However, little is known to date about the psychological needs of SM cancer survivors. The objective of this systematic review was to identify whether SM cancer survivors experience disparate psychological outcomes compared with heterosexual cancer survivors. PubMed/MEDLINE, PsycINFO, CINAHL, Web of Science, and ProQuest databases were searched systematically to identify studies that compared mental health outcomes between SM and heterosexual survivors. A standardized data extraction form was used to extract data from eligible articles. The Joanna Briggs Institute Checklist for Analytical Cross Sectional Studies was used to assess study quality. Twelve studies met the inclusion criteria and assessed distress, depression, anxiety, perceived stress, and mental and emotional quality of life (QOL). Most studies enrolled survivors diagnosed either with female breast cancer or with prostate cancer. Most studies reporting on mental health among women found no differences between SM and heterosexual survivors. Studies conducted among men found that SM survivors experienced higher distress, depression, and anxiety, and lower emotional/mental QOL than heterosexual survivors. The findings of the present synthesis suggest that mental health disparities may exist among SM men diagnosed with cancer, particularly prostate cancer. More research is required to identify mental health disparities among SM survivors diagnosed with other cancers, as well as predisposing and protective factors. In addition, mental health screening and interventions are needed for SM men after cancer diagnosis.