Since 2002, Thailand's Universal Coverage Scheme (UCS) has adopted a comprehensive benefits package with few exclusions. A positive-list approach has gradually been applied, with pre-exposure prophylaxis (PrEP) of HIV recently being included. Disagreements resulting from competing values and diverging interests necessitate an emphasis on procedural fairness when making any decisions. This qualitative study analyses agenda setting, policy formulation and early implementation of PrEP from a procedural fairness lens. Literature reviews and in-depth interviews with 13 key stakeholders involved in PrEP policy processes were conducted. Civil society organizations (CSOs) and academia piloted PrEP service models and co-produced evidence on programmatic feasibility and outcomes. Through a broad stakeholder representation process, the Department of Disease Control proposed PrEP for inclusion in UCS benefits package in 2017. PrEP was shown to be cost-effective and affordable through rigorous health technology assessment, peer review, use of up-to-date evidence and safe-guards against conflicts of interest. In 2021, Thailand's National Health Security Board decided to include PrEP as a prevention and promotion package, free of charge, for the populations at risk. Favourable conditions for procedural fairness were created by Thailand's legislative provisions that enable responsive governance, notably inclusiveness, transparency, safeguarding public interest and accountable budgetallocations; longstanding institutional capacity to generate local evidence; and implementation capacity for realisation of procedural fairness criteria. Multiple stakeholders including CSOs, academia and the government deliberated in the policy process through working groups and sub-committees. However, a key lesson from Thailand's deliberative process concerns a possible 'over interpretation' of conflicts of interest, intended to promote impartial decision-making, which inadvertently limited the voices of key populations represented in the decision processes. Finally, this case study underscores the value of examining the full policy cycle when assessing procedural fairness, since some stages of the process may be more amenable to certain procedural criteria than others.