Objective: The aim was to evaluate the impact of the coronavirus disease 2019 (COVID-19) pandemic and stringent social isolation measures on patients with rheumatic disease (RD) from the beginning of the pandemic (April 2020). Methods: In this UK-based single-centre, prospective, observational cohort study, all RD follow-up patients at our centre were invited by SMS text message in April 2020 to participate in the study. Participants completed questionnaires at four time points between April 2020 and December 2021. We collected demographics, clinically extremely vulnerable (CEV) status, short form 12 mental (MCS) and physical health component scores (PCS) for health-related quality of life, vaccination status, COVID-19 infection rates and incidence of long COVID. Results: We enrolled 1605 patients (female, 69.0%; CEV, 46.5%); 906 of 1605 (56.4%) completed linked responses to our final questionnaire. MCS improved (+0.6, P < 0.05), whereas PCS scores deteriorated (-1.4, P < 0.001) between April 2020 and December 2021. CEV patients had worse mental and physical health scores than non-CEV patients at entry (PCS, 36.7 and 39.3, respectively, P < 0.001; MCS, 40.9 and 43.0, respectively, P < 0.001) and at each time point throughout the study; both mental and physical health outcomes were worse in CEV compared with non-CEV patients (P < 0.001 and P = 0.004, respectively). At study close, 148 of 906 (16.3%) reported COVID infection, with no difference in infection, vaccination or long COVID rates between CEV and non-CEV patients. Conclusions: Mental and physical health in RD patients has changed throughout the pandemic; outcomes for both metrics of health were worse in CEV patients, although there were no differences in infection rates between the groups. These data might assist the understanding and planning of future health-care policy and social restrictions in RD patients. Trial registration: ClinicalTrials.gov, www.clinicaltrials.gov, NCT04542031.