Background: Suicide is a leading cause of death for adolescents, and school connectedness is a potential, modifiable protective factor for suicide. We sought to examine if school connectedness protected against suicide among high school students and if potential moderators affected the relationship between school connectedness and suicide. Methods: We searched online databases (PubMed, EMBASE, CINAHL, and PsycINFO) on December 12, 2021, for studies that examined the effects of school connectedness on suicide among high school students. Results: This systematic review identified 34 studies that examined the effects of school connectedness on adolescent suicidality. Results indicated mixed findings of school connectedness on suicidality. Among studies that assessed a suicide ideation outcome, 73.3% found that school connectedness protected against suicide. Among studies that assessed a suicide attempts outcome, 50% found that school connectedness protected against suicide. Most included studies did not control for notable variables in their final models, such as sleep, impulsivity, substance use, or depression. No studies examined moderators of school connectedness and suicide. Conclusions: School connectedness is somewhat protective of suicidality, and more protective of suicidal ideation than suicide attempts. Researchers should examine the construct of school connectedness among modern youth to better understand school connectedness and suicide.