Introduction Cardiovascular diseases are the most common cause of death in Germany and among the most frequent reasons for encounters in primary care. Most patients with cardiovascular risks (CVRs) have difficulties implementing health-promoting behavioural changes. In this study, a complex intervention containing evidence-based patient materials and structured follow-up consultations are intended to strengthen patients' self-management to improve health behaviour. Methods and analysis In this cluster randomised controlled trial, we investigate the effects of the intervention "Decision aid, action planning and follow-up support for patients to reduce the 10-year risk of cardiovascular diseases"(DECADE) using a 2×2 design. All patients, including the control group (CG), receive a CVR calculation. Three intervention groups (IGs) receive one or both of two different components of the DECADE intervention: IG1 (patient materials), IG2 (follow-up consultations) and IG3 (patient materials and follow-up consultations). The study was planned to be conducted with 77 general practitioners in 3 German regions and a target sample size of 924 patients. The observation period for each patient amounts to 12 months with three patient surveys: baseline (t0), after 6 and 12 months (t1 and t2). The primary outcome is patient activation (Patient Activation Measure 13 (PAM13-D)) at t1. Secondary outcomes include PAM13-D at t2 and further patient-reported and clinical outcomes at t1 and t2. We will also analyse the cost-effectiveness of the intervention, the degree of usage and satisfaction with the intervention. Ethics and dissemination The study was first approved by the lead ethics committee of the University of Freiburg on 15 April 2021 (vote number: 21-1078) and subsequently by the other ethics committees in the study regions (Ethics committee of medical association Baden-Württemberg (B-F-2021-078), Ethics Committee of the Technische Universität Dresden, Dresden (BO-EK-251052021), Ethics Committee of the State Chamber of Physicians of Saxony (EK-BR-92/21-1), Ethics Committee of the Hamburg Medical Association (2021-200013-BO-bet)). Informed consent is required for patients to participate in the study. The results of this study will be published in peer-reviewed journals and presented at congresses by the DECADE team. The DECADE lead management will communicate the results to the funder of this study. Trial registration number German Clinical Trials Register, DRKS00025401 (registration date: 21 June 2021); International Clinical Trials Registry Platform, DRKS00025401.