Sexual and gender minority youth (SGMY) are at greater risk than their heterosexual and cisgender counterparts for suicidal thoughts and behaviors (STB) and nonsuicidal self-injury (NSSI). Unique stressors (i.e., minority stressors) specific to SGMY's stigmatized identities such as discrimination or concealment of one's identity are posited to explain these disparities. However, there is limited research examining the associations among minority stressors, affective mediating processes, and STB and NSSI in SGMY's daily lives. We conducted a 28-day daily diary study to test the mediating effects of daily negative and positive affect and emotion dysregulation between minority stressors and STB and NSSI among SGMY who were recruited from clinical and community settings. Participants were 92 SGMY, aged 12-19 years old (M = 16.45; SD = 1.81; 64% cisgender; 69% White). Results indicated that on days SGMY experienced external and internalized minority stressors, they reported greater intensity of suicidal and nonsuicidal self-injurious ideation and affective distress (i.e., greater negative affect, lower positive affect, and more emotion dysregulation). Greater affective reactivity processes were associated with greater suicidal and nonsuicidal self-injurious ideation intensity on the same day. Most of the within-person associations between external and internalized minority stressors and ideation intensity were mediated by heightened negative affect and emotion dysregulation but not lower positive affect. Our results provide the first evidence of these associations among SGMY, advance the minority stress model, and have implications for clinical interventions as we identified modifiable affective mechanisms. General Scientific SummaryOn days sexual and gender minority youth experience greater than their usual minority stressors, such as discrimination, microaggressions, identity concealment, and internalized stigma, they report greater intensity of their thoughts of suicide and nonsuicidal self-injury (NSSI) and more emotional distress and dysregulation (i.e., greater negative affect, lower positive affect, and more emotion dysregulation). Emotional distress and dysregulation are also associated with greater intensity of thoughts of suicide and NSSI on the same day. The within-person associations between daily minority stressors and intensity of thoughts of suicide and NSSI were mostly accounted for by negative affect and emotion dysregulation but not positive affect.