Defence Healthcare Engagement (DHE) describes the use of military medical capabilities to achieve health effects overseas through enduring partnerships. It forms a key part of a wider strategy of Defence Engagement that utilises defence assets and activities, short of combat operations, to achieve influence. UK Defence Medical Services have significant recent DHE experience from conflict and stabilisation operations (e.g. Iraq and Afghanistan), health crises (e.g. Ebola epidemic in Sierra Leone), and as part of a long-term partnership with the Pakistan Armed Forces. Taking a historical perspective, this article describes the evolution of DHE from ad hoc rural health camps in the 1950s, to a modern integrated, multi-sector approach based on partnerships with local actors and close civil-military cooperation. It explores the evidence from recent UK experiences, highlighting the decisive contributions that military forces can make to healthcare leadership and quality of care overseas, particularly when conflict and health crisis outstrips the capacity of local healthcare providers to respond. Lessons identified include the need for long-term engagement with partners and the requirement for DHE activities to be closely coordinated with humanitarian agencies and local providers to prevent adverse effects on the local health economy and ensure a sustainable transition to civilian oversight.