Infancy and early childhood are periods of dietary transition. Early exposure to specific foods and the establishment of dietary habits during this period can shape long-term food preferences and have lasting effects on health. This study aimed to examine the longitudinal trajectories of sugar-sweetened beverage (SSB) intake in Australian children from birth to age 3 years and identify early-life and socioeconomic factors influencing those trajectories. Mother–infant dyads (n = 934) from the Healthy Smiles Healthy Kids birth cohort study were interviewed on their weekly frequency of SSB intake at 4-month, 8-month, 1-year, 2-year, and 3-year age points. Group-based trajectory modelling analysis was performed to identify trajectories for SSB intake among Australian children. A multivariable logistic regression was performed to identify the maternal and child-related predictors of resulting trajectories. The intake of SSBs showed two distinct quadratic trajectories (high and low) with age. While the two trajectories remained distinctive throughout, the SSB consumption for both groups consistently increased between 4 months and 2 years of age and subsequently stabilised. Compared to low SSB consumers (75%), the high SSB consumers (25%) were significantly more likely to be living in households with three or more children (relative risk (RR): 1.59, 95%CI: 1.02–2.48), had low maternal education (left school < year 12—RR: 1.75, 95%CI: 1.09–2.81; completed year 12—RR: 1.57, 95%CI: 1.02–2.81), and resided in highly/the most socioeconomically disadvantaged areas (highly disadvantaged—RR: 1.89, 95%CI: 1.13–3.18; most disadvantaged—RR: 2.06, 95%CI: 1.25–3.38). Children’s SSB intake patterns are established early in life as they transition from infancy to preschool age, and the trajectories of intake established during early childhood are strongly influenced by socioeconomic factors. Hence, interventions targeted to limit SSB intake and improve nutrition amongst children should occur in early life.