Pandemic influenza represents an ongoing public health threat. Understanding the associated behavioural domain is vital for future intervention development. Cross-sectional qualitative research employing purposive sampling employed a combination of one-to-one semi-structured interviews (n = 57) and focus groups (n = 59). Data were analysed using (1) inductive thematic analysis and (2) theoretical thematic analysis focusing upon resonance with psychosocial and sociocultural constructs. Two broad themes highlighted an important duality regarding the determinants of pandemic behaviour: (1) psychosocial determinants (e.g. agency, cognitions and identity) and (2) sociocultural determinants (e.g. social context and capacity). These findings suggest this duality should shape future intervention development.