This study aimed to evaluate the early introduction of ultra-processed foods (UPF) and identify its association with overweight and anaemia in Brazilian children living in a situation of social vulnerability. A population-based cross-sectional study was conducted in a Brazilian capital. Children aged 12-59 months were included. The presence of overweight and anaemia was evaluated, as well as the introduction of twelve different UPF in children’s first year of life. Association analysis was performed using Poisson regression, with robust estimates of variances. A total of 561 children were studied; 85·5 % had consumed at least one UPF evaluated in the first year of life; 19·1 % were overweight and 52·0 % were anaemic. Adjusted multivariate analyses identified that the early introduction of soft drinks (Prevalence Ratio (PR) = 1·18, 95 % CI (1·02, 1·38)), packaged snacks (PR = 1·17, 95 % CI (1·05, 1·30)) and powdered soft drinks (PR = 1·36, 95 % CI (1·16, 1·60)) increased the likelihood of children being overweight, and the early introduction of chocolate drink (PR = 1·25, 95 % CI (1·02, 1·53)) increased the likelihood of them being anaemic, when comparing children who consumed these UPF before reaching 1 year of age with those who consumed these foods at 12 months of age or older. From the results found, one can see the existing relationship between the early introduction of UPF with overweight and anaemia, being necessary to intensify public health policies to combat malnutrition, focusing on the promotion of proper and healthy eating, especially during the phase of food introduction, focusing on the population living in socially vulnerable situations.