Abstract Background The current study aimed to longitudinally examine whether intrapersonal stigma (i.e., internalized stigma; identity concealment) mediates the associations between interpersonal stigma (i.e., adulthood and childhood victimization; everyday discrimination; perceived external stigma) and mental health outcomes among sexual minority adults, and as a function of two moderators: structural climate and generation. Methods Data from 600 sexual minorities across three generations (i.e., ages 18-25, 34-42, 48-55) who completed all three waves of the 2016-2019 Generations Study were merged with census division data on legal climate (2016 Human Rights Campaign State Equality Index). A series of three-wave time-lagged simplex moderated mediation models were estimated for each independent and dependent variable combination through two parallel mediators, with both moderators included on each independent-mediator variable pathway. Results Greater identity concealment partially explained the effects of perceived external stigma on greater psychological distress and suicidal ideation, but most strongly among older generations. Other mediation was not supported. Reversed sensitivity analyses revealed how identity concealment’s positive effect on suicidal ideation may be suppressed through lower adulthood victimization and, only among younger generations in higher stigma climates, how it’s positive effects on psychological distress and suicidal ideation may be suppressed through lower everyday discrimination. Conclusions Identity concealment may represent a salient mechanism through which sexual minorities navigate structural climates and the harmful effects of interpersonal stigma on distress and suicidal ideation. While the longitudinal findings provide some support for the cross-level effects of sexual minority stigma on mental health outcomes, further advanced time-lagged examinations are warranted.