Abstract Background Palliative sedation refers to the proportional use of titrated medication which reduces consciousness with the aim of relieving refractory suffering related to physical and psychological symptoms and/or existential distress near the end of life. Palliative sedation is intended to be an end of life option that enables healthcare professionals to provide good patient care but there remains controversy on how it is used. Little is known about decision-making processes regarding this procedure. The aim of this study was to explore decision-making processes in palliative sedation based on the experiences and perceptions of relatives and healthcare professionals. Methods We conducted a qualitative interview study with dyads (a bereaved relative and a healthcare professional) linked to 33 deceased patient with cancer who had palliative sedation, in seven in-patient palliative care settings in five countries (Belgium, Germany, Italy, the Netherlands, and Spain). A framework analysis approach was used to analyse the data. Results Two main themes are defined: 1) Decision-making about palliative sedation is a complex iterative process, 2) Decision-making is a shared process between the patient, healthcare professionals, and relatives. Decision-making about palliative sedation appears to follow an iterative process of shared information, deliberation, and decision-making. The patient and healthcare professionals are the main stakeholders, but relatives are involved and may advocate for, or delay, the decision-making process. Starting palliative sedation is reported to be an emotionally difficult decision for all parties. Conclusions As decision-making about palliative sedation is a complex and iterative process, patients, relatives and healthcare professionals need time for regular discussions. This requires a high level of engagement by healthcare professionals, that takes into account patients’ wishes and needs, and helps to facilitate decision-making.