Sport can provide many health benefits to transitioning university students. The Theory of Planned Behaviour (TPB; Ajzen, 1991) has been applied to understand an array of health behaviours. However, past behaviour has been shown to have significant effects on future behaviour. The study examined the relationship between TPB constructs and past behaviour relating to sports participation. A prospective correlation design was used with two waves of data collection. Transitioning students (N = 286) completed assessments of TPB constructs and past behaviour. Four-weeks later measures of sports participation were taken. Two structural equation models were conducted; Model 1 tested the influence of TPB constructs on behaviour and Model 2 included past behaviour. Model 1 accounted for 59% of the variance in intention and 42% in behaviour, which increased to 68% and 43%, respectively, in Model 2. Both models supported TPB propositions. Additionally, in Model 2 past behaviour had a total effect on behaviour and a direct effect on all TPB constructs. The effects of past behaviour on intention and behaviour were mediated by TPB constructs. The study found the TPB explained transitioning students’ participation in sport. Interventions should target the conscious, deliberative factors underlying sport rather than habitual, automatic factors.