As China’s drug policy increasingly prioritizes rehabilitation, social work services have increasingly been integrated into this judicial-led sphere. However, limited attention has been paid to how antidrug social workers navigate their professional autonomy, especially from a processual and diachronic lens to understand changes. Drawing on the theoretical framework of processual legal consciousness, this study examined the professional trajectories of seventeen antidrug social workers across seven different community-based rehabilitation programs in M city. We identified three interlinked stages for their development of professional autonomy: (1) legal estrangement, shaped by project-based and bureaucratic structures that fostered a sense of alienation; (2) legal proximity, marked by a gradual rapprochement with the legal system through rethinking professional roles; and (3) legal mobilization, wherein social workers strategically employed legal discourse to advocate for clients’ rights and expand their professional agency within the judicial–community nexus. We further reconceptualized autonomy as a sustained practice rather than a static state, highlighted the adaptive, strategic, and context-sensitive nature of antidrug social workers’ processual professional autonomy in the context of China, and reflected on its implications for antidrug social work practices and policy amendments.