The developmental timing of suicide-related disparities between heterosexuals and sexual minorities (i.e., lesbian/gay and bisexual (LGB) people) is an understudied area that has critical prevention implications. In addition to developmentally situated experiences that shape risk for suicidality in the general population, sexual minorities also experience unique social stressors (e.g., anti-LGB stigma) that may alter their risk for suicidal behavior at different ages. Using a nationally representative US sample of adults, we assessed age-varying rates of suicidal behavior among heterosexuals and sexual minorities ages 18 to 60 and the age-varying association between anti-LGB discrimination and suicidal behavior. We also tested whether these age-varying prevalences and associations differed for men and women and for sexual minorities who did and did not endorse a sexual minority identity. Results indicate a critical period for suicide behavior risk for sexual minorities during young adulthood, with the highest rates of risk at age 18 followed by a steady decline until the early 40s. Disparities were particularly robust for sexual minorities who identified as lesbian, gay, or bisexual. This pattern was present for both men and women, though sexual minority women in their 30s were more likely to report suicidal behavior than heterosexuals and sexual minority men. Sexual minorities who experienced anti-LGB discrimination were more likely to report suicidal behavior, but the significance of this association was limited to those under 30. The effect of discrimination on suicidal behavior was stronger among young adult sexual minority men, relative to sexual minority women, but was present for a wider age range for sexual minority women (until age 30) relative to sexual minority men (until age 25).