BACKGROUND: There is an urgent need to understand explanatory factors of poor mental health before (pre-) and during (peri-) the COVID-19 pandemic in university students, especially those from underrepresented and minority groups. AIMS: To examine potential differences and explanatory factors for psychological distress, clinical risk and impact of problems on academic outcomes pre- and peri-pandemic in university students. METHOD: A repeated cross-sectional design was used with routine data between August 2018 and July 2022 at the registration stage from a student counselling and mental health service at a UK university. Wilcoxon signed-rank tests were used to examine pre- and peri-pandemic differences in outcomes. Unadjusted and adjusted linear regression models were conducted to assess potential explanatory factors for poor outcomes. RESULTS: A total of 9517 university students had completed sociodemographic and outcome data and were included in analysis. Psychological distress and impact of problems on academic outcomes were not significantly different between pre- and peri-pandemic groups. Clinical risk was significantly higher in the pre-pandemic than peri-pandemic group. Potential explanatory factors for poorer outcomes included being younger, female or non-binary/genderqueer, sexual minority, from a minority ethnic group, having home fee status and having a disability registration. CONCLUSIONS: Poor student mental health profiles and related explanatory factors may not have changed drastically between pre- and peri-pandemic. Longitudinal methods and intersectional approaches should be used in future research. Further understanding of how universities and student mental health services can most efficiently and effectively support the mental health of university students is crucially warranted.