Background: Optimal nutrition during early childhood, including dietary fibre intake, is important for children’s health and development. Knowledge of fibre intake and its determinants in early childhood is limited. We aimed to describe fibre intake and sources and to identify trajectories of fibre intake at age 9, 18, 42, and 60 months and its child and maternal determinants. Associations between fibre trajectory groups and BMI z-scores and child overweight status were also assessed. Methods: This is a secondary analysis of longitudinal data from the Melbourne InFANT Program, trial registration: Current Controlled Trials (ISRCTN81847050). Group-based trajectory modelling was used to identify trajectories of fibre intake from ages 9 to 60 months (n = 503). Multivariable logistic or linear regression was used to assess the determinants of fibre intake trajectories and the association between fibre intake trajectories and obesity outcomes. Results: Four fibre intake trajectory groups were identified, with three groups following stable, rising trajectories of “Low” (52.3%), “Moderate” (32.2%), and “High” (13.3%), respectively. The remaining followed an “unstable” trajectory (2.2%). Girls versus boys were more likely to follow the “Low” fibre intake trajectory, whereas children who were breastfed for ≥6 months and whose mother had a university education were less likely to follow the “Low” fibre trajectory. No association was found between fibre trajectory groups and obesity outcomes. Conclusion: Most children followed a stable, rising trajectory of low fibre intake in early childhood. Child sex, breastfeeding duration and maternal education were significant determinants of low fibre intake trajectory.