Cancer and mental ill-health constitute leading public health problems in Europe, with more than 80 million people reporting mental health issues in Europe and around 4 million new cases of cancer diagnosed per year. People with mental ill-health, have higher cancer incidence and reported mortality, an excess linked to risky health behaviours as well as significant barriers experienced when accessing the often highly fragmented health care systems. Timely and evidence-based preventive strategies including optimizing health care pathways provide a solution to the high cancer morbidity and could improve overall health outcomes in this disadvantaged population. The aim of the Co-CAPTAIN project is to deliver an innovative solution based on the Patient Navigation Model. The Patient Navigation Model is an evidence-based patient-centred intervention which supports patient empowerment through removal of systemic barriers, providing social support and promoting timely access to primary prevention services. Co-CAPTAIN includes partner organizations with long-standing experience in the field of health and social care for people with mental ill-health in the south, east, northwest and central Europe, as well as academic institutions and local governments. Based on implementation science know-how and using the Consolidated Framework for Implementation as well as the Research and the Reach, Effectiveness, Adoption, Implementation and Maintenance frameworks, the Co-CAPTAIN project aims to reduce the gap in health inequalities for people with mental ill-health by reducing cancer burden and improving overall health, which will, in turn, reduce associated costs across health and social care systems in Europe. Moreover, the Co-CAPTAIN project aims to harness the transformative potential of the integrated care pathways in cancer as well as provide health and social care policy recommendations for the adoption and implementation of the Patient Navigation Model across Europe. This action is part of the Cancer Mission cluster of projects on ‘Prevention and early detection’.