The current study investigated key beliefs related to decisions for physical activity (PA) engagement among first-in-family (FIF) students transitioning to university. FIF students (n = 157) completed an online questionnaire assessing standard theory of planned behaviour constructs and belief-based items. One week later, participants completed a follow-up questionnaire assessing self-reported PA during the previous week. Results identified a range of behavioural, normative, and control beliefs that were significantly correlated with both PA intention and behaviour. Various key beliefs were also identified in relation to FIF students' decisions to be regularly physically active, with behavioural beliefs such as "take up too much time", normative beliefs including "friends outside of university", and control beliefs such as "cost", identified. Finally, frequencies of those who strongly or fully accepted these beliefs were analysed, demonstrating that typically, a large number of FIF students did not hold the beliefs, and as such, these are relevant to target in resultant interventions. The current study effectively highlights a number of key beliefs that can be targeted in programs aimed at encouraging FIF students' PA. Further, the study addresses a gap in the literature of targeting FIF students, a cohort at risk for inactivity, and utilises a sound theoretical framework to identify the unique set of beliefs guiding decisions for PA for this at-risk community group.