Background In adults with an intellectual disability, health‐related quality of life (HRQoL) is often measured by proxy report. This cross‐sectional study investigated whether the mental health of proxy raters impacts the way they rate HRQoL. Methods In this study, 110 carers of adults with an intellectual disability completed measures of psychological distress (Kessler‐6) and HRQoL (EQ‐5D‐3L) about their own HRQoL and that of the care recipient. Differences between HRQoL scores as rated by the carer about themselves and the care recipient were calculated (convergence scores) and multiple regression models were fitted to estimate the association between proxy psychological distress and convergence scores for subjective/objective HRQoL controlling for support needs of the care recipient, carer age and gender of care recipient. Results There was a significant association between psychological distress and subjective HRQoL convergence scores (r = .92; P = 0.03; 95%; CI: −1.76 to −0.09). There was no association between psychological distress and objective HRQoL convergence scores (r = .01; CI −0.02 to 0.001; P = 0.08). The association between psychological distress and HRQoL scores was no longer present when models did not include convergence scores. Conclusions Carers experiencing more psychological distress tended to rate their own and the care recipients' subjective HRQoL more similarly. Objective HRQoL measures did not show this convergence in scores with increasing carer psychological distress. Findings differed when the analysis approach was changed, suggesting the results above require replication in future studies.