Volunteers are a popular unpaid support role in end of life care yet how accompaniment influences the dying is underdeveloped. This study examined how companionship works, for whom, in what circumstances and why. Initial realist ideas were developed through participant observation (14 months), document analysis, and realist interviews with companionship trainers (n = 6). Theory testing involved volunteer interviews (n = 7), accounts from the dying, proxy accounts for the dying, and written reflections from companionship training. Companionship helps people live well until they die, prepare for death, and experience a good death. Four areas of volunteering explain these outcomes namely a loving friend, a holistic presence, a non-judgmental intermediary, and wrap around care. The four areas activate mechanisms related to reminiscing, preserving dignity/personhood, and easing suffering, contingent on specific contexts. The findings unpack how volunteering exerts its influence and what contextual factors facilitate outcomes, advancing the knowledge in this area.