This systematic review identified 10 process evaluation studies of positive youth development (PYD) programmes for disadvantaged young people, and aimed to assess the quality of reporting, methods used, and barriers and enablers to delivering programmes as intended. Four databases were searched: Web of Science, Psych INFO, Scopus, and Embase. Results indicated the methods used and quality of the process evaluations were highly varied. Numerous barriers (sessions feeling too much like school, lack of behaviour management skills, lack of funding, and logistical challenges) and enablers (collaboration with the local community, meeting young people's needs, and communication) to delivering programmes as intended were identified. There is a clear need for improvement in design and reporting of process evaluations (e.g., more mixed method design of process evaluations, information on staff training, authors' philosophical standpoint) in studies of PYD programmes for disadvantaged young people alongside a greater awareness of barriers and enablers to programme delivery. Doing so will enable programme outcomes to be appropriately attributed to what is actually delivered and generate more holistic understanding of the extent and reasons that programmes are delivered as intended. This will support more effective programme design, implementation, and sustainability of future PYD programmes for disadvantaged young people.