IMPORTANCE: In the US, recent legislation and regulations have been considered, proposed, and implemented to improve the quality of treatment for opioid use disorder (OUD). However, insufficient empirical evidence exists to identify which policies are feasible to implement and successfully improve patient and population-level outcomes. OBJECTIVE: To examine expert consensus on the effectiveness and the ability to implement state-level OUD treatment policies. EVIDENCE REVIEW: This qualitative study used the ExpertLens online platform to conduct a 3-round modified Delphi process to convene 66 stakeholders (health care clinicians, social service practitioners, addiction researchers, health policy decision-makers, policy advocates, and persons with lived experience). Stakeholders participated in 1 of 2 expert panels on 14 hypothetical state-level policies targeting treatment engagement and linkage, evidence-based and integrated care, treatment flexibility, and monitoring or support services. Participants rated policies in round 1, discussed results in round 2, and provided final ratings in round 3. Participants used 4 criteria associated with either the effectiveness or implementability to rate and discuss each policy. The effectiveness panel (n = 29) considered policy effects on treatment engagement, treatment retention, OUD remission, and opioid overdose mortality. The implementation panel (n = 34) considered the acceptability, feasibility, affordability, and equitability of each policy. We measured consensus using the interpercentile range adjusted for symmetry analysis technique from the RAND/UCLA appropriateness method. FINDINGS: Both panels reached consensus on all items. Experts viewed 2 policies (facilitated access to medications for OUD and automatic Medicaid enrollment for citizens returning from correctional settings) as highly implementable and highly effective in improving patient and population-level outcomes. Participants rated hub-and-spoke-type policies and provision of financial incentives to emergency departments for treatment linkage as effective; however, they also rated these policies as facing implementation barriers associated with feasibility and affordability. Coercive policies and policies levying additional requirements on individuals with OUD receiving treatment (eg, drug toxicology testing, counseling requirements) were viewed as low-value policies (ie, decreasing treatment engagement and retention, increasing overdose mortality, and increasing health inequities). CONCLUSIONS AND RELEVANCE: The findings of this study may provide urgently needed consensus on policies for states to consider either adopting or deimplementing in their efforts to address the opioid overdose crisis.