Background: Due to medical advances and an increasingly ageing population, the number of people living with a serious illness is rising. This has major implications for the burden on family members of assisting with care. Support of family caregivers by healthcare professionals is needed to ensure they can provide quality care for people with serious illness. Aim: To investigate how family caregivers of people with serious illness are supported by healthcare professionals in their caregiving tasks. Design/Participants: Population-based cross-sectional survey of bereaved family caregivers of people with serious illness ( N = 3000) who cared for a person who had died 2–6 months before the sample was drawn (November 2019), as identified through three sickness funds in Flanders, Belgium. The survey explored support from healthcare professionals for family caregivers 3 months prior to bereavement. Results: Response rate was 55.0%. Most family caregivers received support from one or more healthcare professionals for family caregiving tasks, ranging from 71% for promoting social interaction to 95% for managing symptoms. The type of support mostly involved providing information. Use of palliative care services was the strongest predictor of such support across physical, psychosocial and practical tasks. Conclusion: Most family caregivers of those with serious illness get some form of support from healthcare professionals for their tasks. However, an empowering support strategy for example one aimed at increasing self-efficacy of the family caregiver is rare and end-of-life communication between healthcare professionals and family caregivers needs improvement.