Irregular and insufficient sleep place youth at risk for adverse psychological and physical health outcomes. Recent research indicates that discrimination constitutes a type of stressor that interferes with adolescent sleep; however, the mechanisms through which discrimination affects sleep are not well understood. This study examined whether ethnic and non-ethnic (i.e., gender, age, and height/weight) discrimination were associated with adolescents’ sleep duration, variability, and quality, and whether loneliness and perceived stress mediated these associations. An ethnically-diverse sample (42% Latino, 29% European American, 23% Asian) of adolescents (N = 316; M age = 16.40 years, 57% girls) reported on their experiences of discrimination, perceived stress, and loneliness. Sleep duration and variability were assessed by actigraphy and sleep quality through self-reports. Ethnic discrimination was related to shorter sleep duration and both ethnic and non-ethnic discrimination were associated with worse sleep quality. Loneliness and perceived stress partially mediated the relation between discrimination and sleep quality. Discriminatory experiences can heighten feelings of loneliness and stress, which, in turn, may contribute to diminished sleep quality during adolescence.