Summary: Fear and uncertainty have worsened mental health outcomes during the COVID-19 pandemic. COVID-19 testing is essential yet underutilised, and many people may experience difficulties accessing testing if the US federal government fails to sustain the testing capacity. To date, limited evidence exists about the role of COVID-19 testing in mental health. We examined the associations of COVID-19 testing uptake with certain mental disorders, through a nationally representative cohort of adults in US post-secondary education ( N = 65 360). Adults with test-confirmed COVID-19 were at significantly lower risk than those with unconfirmed COVID-19 for severe depression, severe anxiety, eating disorders, and suicidal ideation. Findings suggest another potential benefit of public health efforts to encourage COVID-19 testing, namely promoting mental health.