Introduction and Aims: Alcohol consumption among adolescents and young adults is a persistent community concern. Little is known about the short-term effects on the young adult drinker's quality of life (QOL), particularly prior to the first use of alcohol and the effect of alcohol consumption on subsequent QOL assessments. There is a need to know more about the QOL of those who decide to use alcohol in adolescence and the effect of alcohol consumption on young adult QOL. Design and Methods: This is a prospective longitudinal study of a birth cohort. Data were taken from the 14- and 21-year follow ups. At both time points, QOL was indicated by a measure of happiness and satisfaction. Alcohol use was also measured at 14- and 21-year follow ups. At the 21-year follow up, alcohol use disorder (AUD) was assessed using the Composite International Diagnostic Interview. Results: At the 14-year follow up, there was a strong association between QOL and quantity of alcohol consumed. QOL at 14 years also predicted more frequent alcohol use at 21 years of age. Poor QOL at 14 years was a strong predictor of earlier age of onset of an AUD. However, when age of onset of AUD was used to predict subsequent QOL, the associations were weak and inconsistent. Discussion and Conclusion: Poor QOL was associated with the early age of onset of alcohol use and AUDs. Addressing adolescent and young adult QOL may reduce the early onset of alcohol use and its potential for harm. [Fischer JA, Najman JM, Plotnikova M, Clavarino AM. Quality of life, age of onset of alcohol use and alcohol use disorders in adolescence and young adulthood: Findings from an Australian birth cohort.