Background: We explore cognitive and behavioural biases that influence individual’s willingness to engage advance care planning (ACP). Because contexts for the initiation of ACP discussions can be so different, our objective in this study was to identify specific groups, particular preferences or uniform behaviours, that may be prone to cognitive bias in the ACP decision process. Method: We collected data from the Australian general public ( n = 1253), as well as general practitioners (GPs) and nurses ( n = 117) including demographics, stated preference for ACP decision-making; six cognitive bias tests commonly used in Behavioural Economics; and a framing experiment in the context of ACP. Results: Compared to GPs ( M = 57.6 years, SD = 17.2) and the general public (58.1 years, SD = 14.56), nurses on average recommend ACP discussions with patients occur approximately 15 years earlier ( M = 42.9 years, SD = 23.1; p < 0.0001 in both cases). There is a positive correlation between the age of the general population and the preferred age for the initial ACP discussion ( ρ = 0.368, p < 0.001). Our shared decision-making analysis shows the mean share of doctor’s ACP input is viewed to be approximately 40% by the general public, significantly higher than health professionals (GPs and nurses), who believe doctors should only contribute approximately 20% input. The general public show varying relationships (all p < 0.05) for both first ACP discussion, and shared decision-making for five of six cognitive tests. However, for health professionals, only those who exhibit confirmation bias show differences (8.4% higher; p = 0.035) of patient’s input. Our framing experiment results show that positive versus negative framing can result in as much as 4.9–7.0% shift in preference for factors most relevant to ACP uptake. Conclusion: Understanding how GPs, nurses and patients perceive, engage and choose to communicate ACP and how specific groups, particular preferences or uniform behaviours, may be prone to cognitive bias in the decision process is of critical importance for increasing future uptake and efficient future healthcare provision.