Introduction: Despite increasing rates of opioid misuse and hospitalizations, rates of treatment for those with opioid use disorder (OUD) are very low. This study examined the impact of the Patient Protection and Affordable Care Act's (ACA) insurance expansion on improving rates of insurance, health care access, and treatment for those with OUD. Methods: Data on individuals ages 18-64 with OUD come from the 2008-2014 National Survey on Drug Use and Health (N = 4100). Multivariable logistic regression analyses were performed to estimate the trends of health care insurance, treatment and barriers to care across the stages of ACA implementation: pre-ACA (2008-2009), partial-ACA (2010-2013), and national implementation (2014). All models were adjusted for predisposing, enabling, and need factors. Results: In both adjusted and unadjusted comparisons, national implementation of the ACA was associated with significant improvements in outcome measures for those with OUD. Multivariable analyses indicate that, after national implementation, those with OUD were significantly less likely to be uninsured and were less likely to report financial barriers as a reason for not receiving substance use treatment, relative to the pre-ACA period. Individuals were also more likely to receive substance use treatment and were more likely to report that insurance paid for treatment after national implementation of the ACA relative to the pre-ACA period. These results persisted when national implementation was compared relative to partial-implementation. Conclusions: National implementation of the ACA has helped to reduce rates of uninsurance, barriers to care, and improve rates of substance use treatment for those with OUD.