Background: Understanding the determinants of the intensity of informal care may assist policy makers in the identification of supports for informal caregivers. Little is known about the utilization of informal care throughout the palliative care trajectory. Aim: The purpose of this study was to analyze the intensity and determinants of the use of informal care among cancer patients over the palliative care trajectory. Design: This was a longitudinal, prospective cohort design conducted in Canada. Regression analysis using instrumental variables was applied. Setting/participants: From November 2013 to August 2017, a total of 273 caregivers of cancer patients were interviewed biweekly over the course of the care recipient’s palliative care trajectory. The outcome was the number of hours of informal care provided by unpaid caregivers, that is, hours of informal care. Results: The number of hours of informal care increased as patients approached death. Home-based nursing care complemented, and hence, increased the provision of informal care. Patients living alone and caregivers who were employed were associated with the provision of fewer hours of informal care. Spousal caregivers provided more hours of informal care. Patient’s age, sex, and marital status, and caregiver’s age, sex, marital status, and education were associated with the number of hours of informal care. Conclusions: The intensity of informal care was determined by predisposing, enabling, and needs-based factors. This study provides a reference for the planning and targeting of supports for the provision of informal care.