IntroductionIn response to the burden of chronic disease among older adults, different chronic disease self-management tools have been created to optimise disease management. However, these seldom consider all aspects of disease management are not usually developed specifically for seniors or created for sustained use and are primarily focused on a single disease. We created an eHealth self-management application called ‘KeepWell’ that supports seniors with complex care needs in their homes. It incorporates the care for two or more chronic conditions from among the most prevalent high-burden chronic diseases.Methods and analysisWe will evaluate the effectiveness, cost and uptake of KeepWell in a 6-month, pragmatic, hybrid effectiveness–implementation randomised controlled trial. Older adults age ≥65 years with one or more chronic conditions who are English speaking are able to consent and have access to a computer or tablet device, internet and an email address will be eligible. All consenting participants will be randomly assigned to KeepWell or control. The allocation sequence will be determined using a random number generator.Primary outcome is perceived self-efficacy at 6 months. Secondary outcomes include quality of life, health background/status, lifestyle (nutrition, physical activity, caffeine, alcohol, smoking and bladder health), social engagement and connections, eHealth literacy; all collected via a Health Risk Questionnaire embedded within KeepWell (intervention) or a survey platform (control). Implementation outcomes will include reach, effectiveness, adoption, fidelity, implementation cost and sustainability.Ethics and disseminationEthics approval has been received from the North York General Hospital Research and Ethics Board. The study is funded by the Canadian Institutes of Health Research and the Ontario Ministry of Health. We will work with our team to develop a dissemination strategy which will include publications, presentations, plain language summaries and an end-of-grant meeting.Trial registration numberNCT04437238.