AbstractThe move to online learning during COVID-19 deprived first-year students of friendships and other sources of social support that could buffer against stress during their transition to university. These effects may have been worse for international students than domestic students as many were subjected to travel restrictions or quarantine in addition to the usual stressors. This study examined the impact of COVID-19 on social connectedness and mental health of first-year students enrolled in a metropolitan university in Australia. The study involved 1239 students (30.4% international) and used a 3 (cohorts: 2019, 2020, 2021) × 2 (enrolment status: domestic and international) between-group design. Results showed that both loneliness and university belonging were significantly worse during the first year of COVID-19 compared to the year before or after. Contrary to expectation, domestic students were lonelier than international students across all cohorts. Multiple-group memberships did not change. As predicted, loneliness was moderately to highly correlated with the number of stressors, psychological distress, and (lower) well-being, whereas university belonging and multiple-group memberships were related to positive mental health outcomes. These findings highlight the need for initiatives that promote student connectedness and mental health as the university sector recovers from COVID-19.