Objective: We examined whether trajectories of dietary patterns from 6 to 24 months of age are associated with intelligence quotient (IQ) in childhood and adolescence. Methods: Participants were children enrolled in a prospective UK birth cohort (n = 7652) who had IQ measured at age 8 and/or 15 years. Dietary patterns were previously extracted from questionnaires when children were aged 6, 15 and 24 months using principal component analysis. Dietary trajectories were generated by combining scores on similar dietary patterns across each age, using multilevel mixed models. Associations between dietary trajectories and IQ were examined in generalized linear models with adjustment for potential confounders. Results: Four dietary pattern trajectories were constructed from 6 to 24 months of age and were named according to foods that made the strongest contribution to trajectory scores; Healthy (characterised by breastfeeding at 6 months, raw fruit and vegetables, cheese and herbs at 15 and 24 months); Discretionary (biscuits, chocolate, crisps at all ages), Traditional (meat, cooked vegetables and puddings at all ages) and, Ready-to-eat (use of ready-prepared baby foods at 6 and 15 months, biscuits, bread and breakfast cereals at 24 months). In fully-adjusted models, a 1 SD change in the Healthy trajectory was weakly associated with higher IQ at age 8 (1.07 (95%CI 0.17, 1.97)) but not 15 years (0.49 (-0.28, 1.26)). Associations between the Discretionary and Traditional trajectories with IQ at 8 and 15 years were as follows; Discretionary; 8 years -0.35(-1.03, 0.33), 15 years -0.73(-1.33, -0.14) Traditional; 8 years -0.19(-0.71, 0.33)15 years -0.41(-0.77, -0.04)). The Ready-to-eat trajectory had no association with IQ at either age (8 years 0.32(-4.31, 4.95), 15 years 1.11(-3.10, 5.33). Conclusions: The Discretionary and Traditional dietary pattern trajectories from 6 to 24 months of age, over the period when food patterns begin to emerge, are weakly associated with IQ in adolescence.