BACKGROUND: Given the substantive health inequalities in peri-urban communities and the potential for physical activity to promote health in these communities, identifying modifiable physical activity determinants in this population is important. This study explored effects of the peri-urban environment and psychological constructs on physical activity intentions and behavioural automaticity guided by an integrated theoretical framework. METHODS: Peri-urban Australians (N = 271) completed self-report measures of environmental (i.e. physical/social environment, and neighbourhood selection), motivational (i.e. autonomous motivation), and social cognition (i.e. attitudes, norms, and perceived behavioural control [PBC]) constructs, past behaviour, intentions, and automaticity. RESULTS: A well-fitting path analytic model revealed that: autonomous motivation predicted all social cognition constructs; subjective norms and PBC, but not attitudes; autonomous motivation predicted intentions and automaticity; and subjective norms and PBC mediated effects of autonomous motivation on intentions. Of the environmental constructs, only neighbourhood selection was related to intentions, mediated by PBC. CONCLUSIONS: Autonomous motivation is an important correlate of physical activity intentions and automaticity, and subjective norms and PBC also related to intentions. Individuals perceiving a supportive environment were more likely to report positive PBC and intentions. Targeting change in autonomous motivation, and normative and control beliefs may help enhance physical activity intentions and automaticity in peri-urban communities.