Background Despite guideline recommendation of dual antiplatelet therapy (DAPT) in treating ACS, DAPT is underutilized. Our objective was to determine independent predictors of DAPT non-prescription in ACS and describe pattern of DAPT prescription over time. Methods Patients presenting to 41 Australian hospitals with an ACS diagnosis between 2009 and 2016 were stratified according to discharge prescription with DAPT and single antiplatelet therapy (SAPT) or no antiplatelet therapy. Multiple stepwise logistic regression, accounting for within hospital clustering, was used to determine the independent predictors of DAPT non-prescription, defined as discharge with SAPT alone or no antiplatelet agent. Results 8939 patients survived to discharge with an ACS diagnosis. Of these, 6294 (70.4%) patients were discharged on DAPT, 2154 (24.1%) on SAPT and 491 (5.5%) on no antiplatelet agent. Independent predictors of DAPT non-prescription in the overall cohort were: in-hospital CABG (OR 0.09, 95%CI 0.05–0.14), discharge with warfarin (0.10 (0.07–0.14)), in hospital major bleeding (0.48 (0.34–0.67), diagnosis of unstable angina (0.35, (0.27–0.45)), non-ST-elevation myocardial infarction (0.67 (0.57–0.78)) [both vs. ST-segment elevation myocardial infarction], in hospital atrial arrhythmia (0.72 (0.60–0.86)), history of hypertension (0.83 (0.73–0.94)) and GRACE high risk (0.83 (0.71–0.98)). There was an increase in prescription of DAPT and a shift towards ticagrelor over clopidogrel for ACS from 2013 to 2016 (p < 0.0001), but no overall change in the frequency of DAPT prescription over the entire study period. Conclusion This study revealed high-risk ACS subgroups who do not receive optimal DAPT. Strategies are necessary to bridge the treatment gap in ACS antiplatelet management.