Abstract Background and aims Physical activity is a target for early and ongoing cardiovascular health maintenance. However, relationships between life course trajectories of total activity and all comprising domains (leisure, transport, occupational, domestic) with vascular function and structure have not been examined. This study aimed to determine associations between life course activity trajectories and mid-adulthood vascular structure and function. Methods Using the Australian Childhood Determinants of Adult Health Study (four timepoints [ages 9-49y]; 1985 baseline), latent class growth mixture modelling assessed life course trajectories of questionnaire measured total and domain-specific activity (n=2311). Relationships between trajectories and vascular structure (carotid intima-media thickness [n=914], carotid plaques [n=867]), and vascular function (Young’s Elastic Modulus [n=765], carotid distensibility [n=765]) were analysed using log-binomial and multivariable regression adjusted for mid-adulthood body mass index, smoking status, occupation type, area-level socio-economic status, high and low-density lipoprotein cholesterol. Results ‘Consistently high’ leisure activity was associated with reduced risk of plaques (RR=0.56; 95%CI=0.23-0.89). ‘High-increasing’ school/occupational activity was associated with higher carotid intima-media thickness (β=0.06; 95%CI=0.01-0.11). No associations were observed among Young’s Elastic Modulus, carotid distensibility, or transport and domestic activity. Conclusions This study was the first to assess life course trajectories of total and domain-specific activity against vascular structure and function. Findings highlight that maintaining high levels of leisure-time activity across the life course may be associated with better vascular structure in mid-adulthood.