An English competency-based curriculum (CBC) policy has recently been proposed and implemented by the Ministry of Education (MoE) at public sandbox schools in education innovation areas around Thailand. Little is known about CBC policy implementation in Thailand's Deep South. This study explores voices of the key stakeholders--school administrators, teachers, teacher educator and parents--regarding CBC policy implementation in Narathiwat, one of the three southernmost provinces. Drawing upon a reflexive thematic analysis of the interview transcripts of fifteen stakeholders, the findings reveal four key factors underpinning effective English CBC policy implementation: policy implementation at the school level, influence of sociocultural and linguistic contexts, the support of the MoE, and the inclusive engagement of stakeholders. Though this study was conducted in only one southern province, its implications may help policy makers, educational administrators, and relevant parties recognize issues attending the implementation of English CBC in public sandbox schools in all of Thailand's southernmost provinces--this corresponds to the advocacy of equal opportunities and education equity (SDG 4 Quality Education) for all.