Background: Integrating primary prevention into care pathways for older adults is a core strategy of healthy ageing, but evidence remains limited. We aimed to determine whether incorporating a multidomain intervention into primary health care could improve standard value-based health outcomes and quality of life. Methods: For this Taiwan Integrated Geriatric Care (TIGER) study, a pragmatic randomised controlled trial, we recruited community-dwelling outpatients aged 65 years or older with at least three chronic medical conditions. We excluded people with malignancies undergoing chemotherapy, people with a life expectancy of less than 12 months, or people who were insufficiently able to communicate with study staff. Participants were randomly assigned (1:1) to usual care or to the integrated multidomain intervention using block randomisation. The integrated multidomain intervention entailed 16 2-h sessions per year, comprising communal physical exercise, cognitive training, nutrition and disease education, plus individualised treatment by specialists in integrated geriatric care. The primary outcome was changes from baseline quality of life, based on 36-item Short Form Health Survey (SF-36) scores, at 3, 6, 9, and 12 months. Intervention effects were analysed per protocol using a generalised linear mixed model. This trial is registered with ClinicalTrials.gov, NCT03528005. Findings: Between June 25, 2018, and Feb 15, 2019, 628 participants were screened, of whom 398 were assigned to the integrated multidomain intervention (n=199) or to usual care (n=199). 335 (84%) participants completed the 12-month follow-up. Compared with the usual care group, the integrated multidomain intervention group had significantly higher mean SF-36 physical component scores across all timepoints (overall difference 0·8, 95% CI 0·2–1·5; p=0·010), but differences at 3, 6, 9, and 12 months did not reach statistical significance. The SF-36 mental component scores did not differ significantly overall, but were significantly higher in the integrated multidomain intervention group at the 12-month follow-up (55·3 [SD 7·6] vs 57·2 [7·0]; p=0·019). No serious adverse events occurred. Interpretation: Incorporating multidomain interventions into integrated health care improved quality of life. Our standardised protocol is amenable to inclusion in policies to promote value-based care and healthy ageing. Funding: National Health Research Institutes, Taiwan, and Ministry of Science and Technology, Taiwan.