Objective: The aim of this study was to identify potential model of care approaches and systems processes for people presenting to acute healthcare settings with mental health problems, including mental illnesses. Methods: Five (consensus) nominal group technique sessions were conducted in 2019 with a purposive sample of stakeholders from health, police, ambulance and consumer agencies (n = 21). Sessions were recorded, transcribed and analysed for thematic content. Results: Potential model of care approaches and systems processes for people with mental health problems in the emergency department include: a skilled collaborative approach to care; consumer-focused service; knowledge improvement; early assessment; the development of models, systems and processes; and the built environment. In the broader acute care setting, the themes of formal care, linking of services, enhancing informal and innovative care options, improving information sharing and enhancing training and education were identified. Conclusions: Coherent and multifaceted approaches to the provision of care to people with mental health problems and diagnosed mental illnesses who are requiring emergency care include the linking and sharing of systems and information, changing the built environment and exploring new models of service delivery. What is known about the topic?: There is considerable evidence of interventions used in the emergency department and acute healthcare settings for this vulnerable group of people with mental health problems and diagnosed mental illnesses; however, the evidence for appropriate model of care approaches and systems processes is limited. What does this paper add?: For people with mental health problems in emergency departments and for people with diagnosed mental illnesses in acute care settings, targeted directions to further support treatment include the linking and sharing of systems and information, changing the built environment and exploring new models of service delivery. What are the implications for practitioners?: Planning changes to services for mental health clients with acute problems needs to incorporate clinicians, health service planners, architects and a range of emergency services personnel.