From its origins in services for children and families, Family and Group Conferencing (FGC) is being developed in adult social care and mental health contexts. It offers an inclusive process whereby a person and their chosen supporters can devise their own plans in consultation with relevant professionals. Ways of working have evolved significantly, reflecting the different social and legal and contexts of work with adults. Building upon an earlier scoping of the field, a Delphi consultation was employed to consolidate our understanding of ‘how the model should be delivered’, ‘ingredients for success’, and ‘potential positive outcomes’. Three panels of experts were recruited to take part in the consultation, including those with lived experience. Consensus was achieved in relation to thirty-two statements, which provide a basis for fidelity criteria that can be used in future evaluations and trials, and in the development of standards and guidance for FGC practice with adults—both in the UK and internationally. Consensus was not achieved as to whether and how this approach could be offered for an informal carer in circumstances where the person receiving care did not wish or was unable to participate.