Occupation-based interventions use engagement in a person's daily activities to achieve change. There is growing research into the use of occupation-based group interventions in the inpatient rehabilitation setting. It remains unclear whether occupation-based groups offer comparable outcomes to occupation-based interventions delivered individually; this research will precede a clinical trial aimed at comparing these two approaches for improving occupational performance outcomes. This study details the process of co-designing the intervention. Partnering with clinicians and patients in the design of healthcare interventions can promote patient-centred care, enhance uptake, and improve applicability and sustainability of the intervention to that setting. A modified nominal group technique (NGT) design was applied to facilitate two meetings and an electronic survey with an expert panel of clinicians and patients. Twelve participants (n = 4 occupational therapists, n = 1 registered nurse, n = 1 physiotherapist, n = 1 occupational therapy assistant, n = 1 occupational therapy manager, and n = 4 patients) were purposively recruited. A modified approach to the technique's four stages was used: silent generation, round robin, clarification, and voting. Consensus was set at >50%. Qualitative data from group discussions were analysed thematically. All participants agreed the intervention should include patient-centred, goal-directed, practice of daily activities, including breakfast and lunch preparation, domestic tasks, and laundry. Other components that were agreed included where the groups could run, group size, eligibility criteria, and frequency. Key themes from clinicians included needing a goal-directed intervention, focused on progressing towards hospital discharge; time and resource requirements were also discussed. Patients emphasised the importance of building social connections, opportunity to engage in meaningful activity, and the importance of linking participation to patient goals. Through collaboration with clinicians and patients, an occupation-based group intervention considering the available evidence, alongside clinical, experiential, and contextual sources of knowledge was developed; this resulted in an evidence-based, patient-centred, and contextually relevant intervention.