Summary Background Excess body fat is associated with an increase in risk of type 2 diabetes and hypertension in adulthood and these risks can adversely affect progression of arterial disease. We aimed to assess the impact of lifelong patterns of adiposity on cardiovascular risk factors and carotid intima media thickness (cIMT) in later life in participants in the 1946 British birth cohort study. Methods The National Survey of Health and Development Study was a nationally representative sample of 5362 singleton births to married parents in England, Scotland, and Wales, stratified by social class, during 1 week in March 1946. Our present study is based on the 60% of participants still alive and with a known present address in England, Scotland, or Wales who attended a clinic assessment after invitation aged 60–64 years. We included participants with lifetime adiposity measures, cardiovascular risk factors, and cIMT measured at 60–64 years. Participants were classified as normal weight or overweight or obese at each age (36, 43, 53, and 60–64 years) in adulthood, and childhood overweight was defined. Patterns of BMI change were identified and we used BMI to define adiposity status. We used multivariable linear regression to establish the cross-sectional association of BMI category at age 60–64 years with cIMT, adjusted for various confounders. Findings We included 1273 (45%) of 2856 participants eligible in 2006–10 (at age 60–64 years) in this study. Compared with normal weight, overweight and obesity were associated with higher cIMT (0·029 mm, 95% CI 0·014–0·043) and systolic blood pressure (7·95 mm Hg, 5·86–10·0). Increased cIMT, systolic blood pressure, leptin, prevalence of diabetes, and reduced adiponectin were all associated with duration of exposure to adult adiposity (p<0·0001 for all). We noted little additional effect of childhood overweight. Individuals who dropped a BMI category in adulthood had lower cIMT (–0·034 mm, −0·056 to −0·013) and leptin concentrations (–0·4 ng/mL, −0·47 to −0·32), even when this change was not maintained, than did those who never lost weight. Interpretation Longer exposure to high adiposity in adulthood had a cumulative adverse effect on cardiovascular phenotype in later life. Reductions in BMI category, even if not sustained, were associated with decreases in cIMT and improvements in cardiovascular risk-factor profile, suggesting that weight loss, at any age in adulthood, is worthwhile because it might result in long-term cardiovascular benefit. Funding Medical Research Council and the British Heart Foundation.