Background The benefits of comprehensive geriatric assessment (CGA) are well established for hospital care but less so for primary care. Our primary objective was to assess the effect of two multifaceted interventions based on a CGA adapted for primary care on a composite criterion combining all-cause mortality, emergency department visits, unplanned hospital admissions, and institutionalisation. Methods This open-label, pragmatic, three-arm, cluster-randomised controlled trial involved 39 general practices in France. It included 634 patients aged 70 years or over with chronic health conditions and/or an unplanned hospital admission in the past 3 months, between 05/2016 and 08/2018. Interventions were in arm 1: a systematic nurse-led CGA; arm 2: a GP-led CGA, at the GP’s discretion; arm 3: standard care. The primary composite endpoint was assessed at 12 months. The secondary endpoints included: components of the composite endpoint, health-related quality of life (Duke Health Profile), functional status (Katz Activities of Daily Living Index) and medications (number) at 12 months. Pairwise comparisons between the experimental groups and the control were tested. The main analysis was performed on the intention-to-treat (ITT) population, after imputing missing information and adjusting for baseline imbalances by mixed effects regressions. Results For the primary composite outcome, no statistically significant difference was found between arm 1 and the control (adjusted odds ratio [aOR] = 0.81 [95%CI 0.54–1.21], P = 0.31), whereas arm 2 and the control differed significantly (aOR = 0.60 [0.39–0.93], P = 0.022). A statistically lower risk of unplanned hospital admission in arm 2 vs control (aOR = 0.57 [0.36–0.92], P = 0.020)) was observed, while no statistically significant differences were found for the other components and between arm 1 and the control. None of the other secondary endpoints differed between arms. Conclusions Our study led in community-dwelling older patients with chronic conditions found no significant effect of a CGA adapted for primary care on mortality, functional independence and quality of life, but suggests that a GPled CGA may reduce the risk of unplanned hospital admission. Our study demonstrates the feasibility of incorporating CGA into clinical practice and highlights its potential benefits when applied on a case-by-case basis, guided by the GPs who develop the resulting PCP.