The identification of early-life determinants of overweight is crucial to start early prevention. As weight gain accelerates between 2 and 6 years, we studied the association between diet quality in children aged 3 years and the change in BMI and overweight incidence in the following 7 years. From the Dutch GECKO Drenthe birth cohort, 1001 children born in 2006 or 2007 with complete data on diet (food frequency questionnaire at the age of 3 years) and growth at the age of 3 and 10 years were included. Diet quality was estimated with the evidence-based Lifelines Diet Score (LLDS). Measured height and weight at the age of 3 and 10 years were used to calculate BMI z-scores standardized for age and sex. The associations of the LLDS (in quintiles) with BMI-z change and overweight incidence were studied with linear and logistic regression analyses. Overweight prevalence in the total study population increased from 8.3% at the age of 3 years to 16.7% at the age of 10 years. The increase in overweight prevalence ranged from 14.7% in Q1 to 3.5% in Q5. Children with a better diet quality (higher quintiles of LLDS) increased significantly less in BMI-z (confounder adjusted βLLDS = -0.064 (-0.101; -0.026)). Children with a poor diet quality at the age of 3 years had a considerably higher risk for overweight at the age of 10 years (confounder adjusted OR for Q1 vs. Q5 was 2.86 (95% CI 1.34-6.13). These results show the importance of diet in healthy development in the early life following the first 1000 days when new habits for a mature diet composed of food groups with lifelong importance are developed, providing a relevant window for overweight prevention early in life.