Mass media campaigns are increasingly seen as an important part of suicide prevention; however, despite their popularity, their efficacy is not well understood. The current review aimed to address key knowledge gaps regarding how mass media campaigns can be optimized to prevent suicide, by looking at their global efficacy, and mechanisms related to successful outcomes. A systematic review of the international literature examined studies which evaluated mass media campaigns targeted at suicide prevention, where suicide behaviors (mortality, attempts) or suicide literacy (knowledge, attitudes, help-seeking) was identified as a primary outcome. Thirteen articles describing 12 unique campaigns met eligibility criteria. For behavioral outcomes, mass media campaigns appear to be most effective when delivered as part of a multicomponent suicide prevention strategy, while “standalone campaigns” were modestly useful for increasing suicide literacy. Level of exposure, repeat exposure, and community engagement appeared to be fundamental to the success of these campaigns; however, these constructs were poorly adhered to in the development and implementation of campaigns. Overall, the mixed quality of the included studies highlights a need for increased quantity, consistency, and quality of evaluations to advance the evidence base.