Background: Significant social and political changes occurred in the UK between 2015 and 2020. Few studies have examined population level trends in experiencing discrimination and mental health problems during this period. Aims: To determine prevalence trends in perceived discrimination and probable mental health problems amongst UK adults during 2015–2020. Method: Repeated cross-sectional data from the UK Household Longitudinal Study was used to estimate nationally representative trends in perceived discrimination and probable mental health problems (GHQ-12; 4+ threshold) among adults between 2015/2016–2019/2020 (25,756 observations). Weighted logistic regression models with post-estimation margins commands determined changes between survey waves controlling for sociodemographic characteristics. Mediation models explored whether changes in perceived discrimination prevalence trends explained trends in probable mental health problems. Results: From 2015/2016 to 2019/2020 perceived discrimination and probable mental health problems increased significantly by 6·1% (95% CI: 3·4–8·8, p