The COVID-19 pandemic caused financial hardship, social isolation, and distress, increasing risk for adolescent depression. Even before the pandemic, <50% of youth with depression accessed care, and not all benefited from existing treatments. Accordingly, this randomized-controlled trial tested online single-session interventions (SSIs) during COVID-19 in adolescents with elevated depression (N=2,452, ages 13-16). Adolescents recruited via social media were randomized to 1 of 3 SSIs: a behavioral activation SSI, an SSI teaching that personal traits are malleable, or a supportive control. We tested each SSI’s effects on post-intervention (hopelessness, agency) and 3-month outcomes (depression, hopelessness, agency, generalized anxiety, COVID-related trauma). Compared to the control, both active SSIs reduced 3-month depressive symptoms; decreased post-intervention and 3-month hopelessness; and increased post-intervention agency. Several differences between active SSIs emerged. Results confirm the effectiveness of two free-of-charge, online SSIs for adolescents with elevated depression, even in the high-stress context of COVID-19.