Background <p>Physical activity, sedentary behaviour, and sleep (i.e., 24-hour movement behaviours) are among key determinants of health and well-being. However, epidemiological studies that investigate these behaviours while accounting for their co-dependent nature are still scarce. This article describes the protocol of a population-based study that aims to explore the prevalence and correlates of 24-hour movement behaviours among Slovenian adults and their cross-sectional and longitudinal associations with health and well-being.</p> Methods <p>Participants will be recruited through the National Health-related Lifestyle Survey study that is conducted among a national representative sample of Slovenian adults aged 18–74 years (<i>n</i> of invited participants every four years = 17,500). Baseline data collection will include assessment of 24-hour movement behaviours using activPAL accelerometers. Domain-specific movement behaviours, built environment, and well-being will be assessed using questionnaires. A linkage to the National Health-related Lifestyle Survey that include data on demographics (e.g., marital status, socio-economic status), health-related behaviours (e.g., diet, smoking), and health (e.g., self-reported health, comorbidities) will also be established. The follow-up data collections (every four years) will include self-reported assessments of 24-hour movement behaviours, built environment, health and well-being, and linkage to the national health-related registers.</p> Discussion <p>The study will produce new knowledge on 24-hour movement behaviours, their socio-demographic and built environment correlates, and their cross-sectional and longitudinal relationship with health outcomes using compositional data analysis. It will reveal an insight into the relative importance of domain-specific and type-specific movement behaviours, informing future 24-hour movement guidelines for adults.</p>