Aims: To explore healthcare professionals' perceptions of the feasibility and acceptability of family engagement in early mobilisation for adult critically ill patients. Background: Early mobilisation is beneficial to minimise intensive care unit acquired-weakness in critically ill patients and family engagement can help with meeting early mobilisation goals, but it is not widely practiced. Understanding healthcare professionals' perceptions of feasibility and acceptability of family engagement in early mobilisation of adult critically ill patients is required to inform future implementation strategies to promote early mobilisation. Design: A descriptive qualitative study. Methods: Face-to-face, individual, semi-structured interviews were conducted between August 2021 and March 2022 with healthcare professionals working in two intensive care units in Australia. The interviews were analysed using the inductive content analysis, and descriptive statistics were used to summarise participant characteristics. The COREQ checklist was followed when reporting this study. Results: Eleven ICU nurses, five physiotherapists and four physicians participated in the interviews. Three main categories were identified: (i) healthcare professionals' readiness, (ii) mediators of engagement and (iii) foundations for successful implementation. Most participants demonstrated a positive attitude towards an implementation of family engagement in early mobilisation for adult critically ill patients; however, capability and capacity of healthcare professionals, family members' willingness, availability and readiness and the care context were considered factors that could influence the successful implementation. Conclusion: From the perspectives of healthcare professionals, family engagement in early mobilisation is feasible and acceptable to enact but implementation is influenced by contextual factors including, healthcare professionals' capability and capacity and family members' willingness, availability and readiness. Collaborative teamwork and preparing family members and healthcare professionals are needed to support this practice. Relevance to Clinical Practice: The findings provide important information to further identify potential strategies of family engagement in early mobilisation and to help and mitigate factors that impede implementation.