Background The consequences of prolonged exposure to obesity on biomarkers of myocardial stress and injury remain unclear. We examined associations of duration and cumulative severity of obesity from childhood to later adulthood with concentrations of N-terminal pro-B-type natriuretic peptide (NT-proBNP), high-sensitivity cardiac troponin I (hs-cTnI), and growth differentiation factor-15 (GDF-15) at age 62 years. Methods The sample comprised 4,901 participants in the 1958 National Child Development Study who had measurements of NT-proBNP, hs-cTnI, or GDF-15 at age 62 years and at least four BMI assessments between 7 and 62 years of age. Individual BMI trajectories were modelled, from which total duration of obesity and mean excess BMI (area between the trajectory and the age-specific obesity threshold divided by duration) were derived. Associations of ever versus never having been obese, obesity duration, and mean excess BMI with biomarker concentrations were examined using general linear regression models with progressive adjustment for early-life characteristics; contemporaneous cardiometabolic factors; and health behaviours, socioeconomic position, and psychosocial factors. Nonlinear associations of obesity duration were estimated using restricted cubic splines and subsequently approximated using linear splines. Results Overall, 26.3% of participants had ever experienced obesity. There was no evidence of an association between ever versus never having been obese and NT-proBNP. Among men, ever having been obese was associated with 11.00% (95% CI, 4.62-17.37) higher hs-cTnI in the fully adjusted model, whereas there was no evidence of an association among women. Ever having been obese was associated with higher GDF-15, although the association attenuated substantially after adjustment for contemporaneous cardiometabolic factors. Longer obesity duration was associated with higher concentrations of all three biomarkers in fully adjusted models, but the pattern differed by biomarker: hs-cTnI increased approximately linearly with duration, whereas NT-proBNP and GDF-15 remained relatively stable up to approximately 25 years of obesity before increasing with longer duration. In fully adjusted models, each additional year of obesity beyond 25 years was associated with 1.80% (95% CI, 0.54-3.06) higher NT-proBNP and 0.81% (95% CI, 0.25-1.36) higher GDF-15, while each additional year across the full range of obesity duration was associated with 0.41% (95% CI, 0.07-0.76) higher hs-cTnI. Among participants who had ever experienced obesity, each 1 kg/m2 higher mean excess BMI was associated with 4.02% (95% CI, 1.79-6.24) higher NT-proBNP and 2.00% (95% CI, 0.49-3.51) higher hs-cTnI in fully adjusted models; there was no evidence of an association with GDF-15. Conclusions Longer duration of obesity was associated with higher concentrations of biomarkers reflecting myocardial stress, injury, and cellular stress at age 62 years, with associations particularly evident after approximately 25 years of obesity for NT-proBNP and GDF-15. These findings suggest that duration of obesity may provide clinically relevant information beyond current obesity status, supporting its consideration as an additional dimension of cumulative obesity burden in cardiovascular risk assessment.