Complex psychosis is associated with high social and economic costs. The key skills and attributes needed by mental health professionals to provide optimal clinical care to people experiencing complex psychosis have not previously been defined. A framework detailing these skills and attributes is needed to support the identification of training needs for those working with this population. A modified online Delphi method was used to reach consensus on the skills and attributes essential for mental health professionals to deliver optimal clinical care to people experiencing complex psychosis. Participants were international healthcare professionals and academic researchers who self-identified as experts in complex psychosis. Participants were asked to rate their level of agreement with each item on a five-point Likert-type scale and to provide comments. Qualitative feedback was used to modify existing, or create new, items for subsequent rounds. 64 responses were received across three Delphi rounds. 167 items reached consensus and were endorsed (132 in Round 1, 31 in Round 2 and 4 in Round 3). Median score range for endorsed items was 4.5/5, with 88.6% scoring 5/5. All 167 endorsed items were included in the framework, categorised into 14 overarching domains. Multiple skills and attributes were identified as being core components required in the delivery of optimal care by mental health professionals to people experiencing complex psychosis. The resulting framework provides a benchmark for training and skill development of mental health clinicians at both individual and team levels to optimise effective working with this high-needs population.