BackgroundMental health issues are common among patients with chronic physical conditions, affecting approximately one in five patients. Poor mental health is associated with worse disease outcomes and increased mortality. Problem-solving therapy (PST) may be a suitable treatment for targeting poor mental health in these patients. This study protocol describes a randomised controlled trial of the Healthy Mind intervention, a general practice-based intervention offering PST to patients with type 2 diabetes and/or ischaemic heart disease and poor mental well-being.MethodsA stepped-wedge cluster-randomised controlled trial with 1-year follow-up will be conducted in Danish general practice. At the annual chronic care consultation, patients with type 2 diabetes and/or chronic ischaemic heart disease will be screened for poor mental well-being. Patients in the control group will be offered usual care while patients in the intervention group will be offered treatment with PST provided by general practitioners (GPs) or general practice staff, such as nurses, who will undergo a 2-day PST course before transitioning from the control to the intervention group. The primary outcome is change in depressive symptoms after 6 and 12 months. Secondary outcomes include change in mental well-being, anxiety, and diabetes distress (patients with type 2 diabetes) after 6 and 12 months as well as change in total cholesterol levels, low-density lipoprotein (LDL) levels, and blood glucose levels (patients with diabetes) after 12 months. Process outcomes include measures of implementation and mechanisms of impact. We aim to include a total of 188 patients, corresponding to approximately 14 average-sized general practices.DiscussionThe Healthy Mind trial investigates the impact of PST treatment for patients with chronic disease and poor mental well-being in general practice. This will be the first randomised controlled trial determining the effect of PST treatment for patients with chronic diseases in general practice. The results of this study will provide relevant insights to aid GPs, and general practice staff manage patients with poor mental well-being.Trial registrationClinicalTrials.gov NCT05611112. Registered on October 28, 2022.