Background Recent research has not supported the idea that parental supply of alcohol to adolescents prevents later alcohol-related harm. Yet the specific role of parental supply in shaping patterns of drinking over time remains unclear. This study investigated the role of parental supply of alcohol in patterns of drinking across adolescence, and assessed whether that role remained consistent over time. Method Using a longitudinal cohort of 1927 adolescents (mean age 12.9 years), recruited in 2010 and 2011 from schools across Australia and followed up annually until 2016, we assessed three outcomes using mixed-effect negative binomial regression: frequency of consumption, typical quantity consumed, and overall alcohol consumption in the year (frequency * quantity). Child, parental, familial, and peer confounders of adolescent alcohol consumption were measured and adjusted for in the analyses. Findings Parental supply was associated with greater overall consumption in earlier adolescence: Grade 7–8 (incidence rate ratio [IRR]: 3.61; 95% CI: 2.55, 5.12; no supply IRR: 1.00), Grade 8–9 (IRR: 4.84; 95% CI: 3.66, 6.39; no supply IRR: 1.44) and Grade 9–10 (IRR: 8.33; 95% CI: 6.28, 11.05; no supply IRR: 4.75). Alcohol consumption continued to increase in later adolescence regardless of whether parental supply occurred. Conclusions Parental supply of alcohol was associated with increased alcohol consumption by their children during early adolescence. While parental supply appears to have less impact on drinking in later adolescence, there was no evidence to suggest it is protective. Parents should be advised to avoid supplying children with alcohol, particularly in early adolescence.