Social marginalization increases the risk of suicidal ideation (SI) among individuals with diverse identities, yet research examining the effects of marginalization has focused on one identity. Emerging adulthood is a critical period of identity development and the age group with the highest rates of SI. Considering the challenges of living in potentially heterosexist, cissexist, racist, and sizeist environments, we tested whether possessing multiple marginalized identities was associated with severity of SI through factors proposed in the interpersonal–psychological theory (IPT) and the three-step theory (3ST) of suicide and if mediation paths were moderated by sex. A sample of 265 college students completed a cross-sectional online survey assessing SI and constructs related to IPT and 3ST. The number of marginalized identities was generated by adding minoritized sexual orientation, race/ethnicity other than non-Hispanic White, body mass index >25 kg/m2, sexual attraction to same sex but identified as heterosexual, and gender-fluid identity. In IPT multiple mediation analyses, possessing more marginalized identities was associated with SI severity through burdensomeness and hopelessness, but not belonging. Indirect paths through burdensomeness and belonging were moderated by sex. For 3ST, possessing more marginalized identities was associated with SI severity through hopelessness and psychological pain, but not social connection or meaning in life. Future research should consider intersecting social identities and test mechanisms by which multiply marginalized college students develop resilience to SI risk factors, such as support within their marginalized groups, to inform suicide assessment and intervention efforts on college campuses.