Objective Sexual and gender minority (SGM) adults often report a disproportionately high rate of suicidal ideation compared to their heterosexual and cisgender counterparts. The current study aimed to understand the relationship between discrimination for one's sexual orientation or gender identity and suicidal ideation. We hypothesized that discrimination would be associated with suicidal ideation at one's worst point through the indirect effects of hopelessness regarding thwarted belongingness and perceived burdensomeness. Method A sample of 178 SGM adults (M age = 30.34, range 18–69; 76% white) completed an online questionnaire assessing minority-specific stressors and suicide-related thoughts and behaviors. Results A mediation model with bootstrapping indicated that greater discrimination was associated with more frequent suicidal ideation at one's worst point through the indirect effect of hopelessness regarding thwarted belongingness. Conclusions The current study provides evidence that the pathway between discrimination and worst point suicidal ideation may be partially explained by the perception that one will never belong. These findings support the utility of an understudied Interpersonal Theory of Suicide hypothesis for research among SGM adults.