Complementary feeding (CF) and overweight relationships during early childhood are inconsistent in the literature. We described the association of CF during the first year of life with risk of overweight at 24 months of age in the population-based 2004 and 2015 Pelotas (Brazil) Birth Cohorts (2004c and 2015c). CF introduction was evaluated at the 3 and 12 months’ follow-ups by asking mothers using a list of foods. Risk of overweight at 24 months of age was BMI-for-age z-score above +1sd from the median of the WHO 2006 growth standards. Our analyses included 3823 (2004c) and 3689 (2015c) children. Early introduction CF (before 6 months of age) prevalence in 2004c was 93·3 (95 % CI 92·5, 94·1) % and in 2015c was 87·2 (95 % CI 86·1, 88·2) %. Tea was the item introduced earlier in both 2004c (68·8 %) and 2015c (55·7 %). At 6 months of age, vegetable mash was the most introduced food in 2004c (33·5 %) and 2015c (47·9 %). Between 2004c and 2015c, the introduction of fresh milk decreased 82·1 to 60·5 % and yogurt from 94·4 to 78·1 % during the first year. Risk of overweight prevalence at 24 months was 33·0 (95 % CI 31·6, 34·5) % in 2004c and 32·0 (95 % CI 30·5, 33·5) % in 2015c. In 2015c, the adjusted odds of risk of overweight at 24 months were increased 1·66 and 1·50 times with the early introduction of fresh/powdered milk: plus water, tea or juice, and plus semi-solid/solid food groups, respectively. It is essential to reinforce the adherence to global recommendations on timely feeding introduction and encourage exclusive breast-feeding until 6 months of age to prevent child overweight.