This study explores the intricate relationships between Communicative Language Teaching (CLT) practices, learners' professional backgrounds, cultural diversity, and student engagement within English for Specific Purposes (ESP) education. The sample comprises 1,243 Chinese learners who are studying English for Specific Purposes. The findings demonstrate that meaning-based CLT classroom practices significantly enhance student engagement, affirming the efficacy of approaches prioritizing authentic communication and practical language use in fostering active participation. However, the impact of these practices is not uniform; it varies depending on the professional background of the learners, suggesting that pedagogical strategies must be tailored to accommodate the diverse needs of students from different fields. Additionally, cultural diversity was identified as a critical factor in promoting student engagement, with the exchange of varied perspectives enriching the learning environment. Interestingly, while cultural diversity positively influenced overall engagement, it did not significantly moderate the relationship between CLT practices and student engagement, indicating that the benefits of CLT practices are consistent across culturally diverse settings. The study also highlighted challenges linked to specific professional backgrounds, where discrepancies between learners' prior knowledge and the demands of ESP course content could lead to reduced engagement. This underscores the necessity of aligning language instruction with learners' professional contexts to ensure content relevance and applicability. The findings suggest that educators must consider professional and cultural factors when designing CLT-based ESP courses to create more inclusive and engaging learning environments. Future research should further investigate these dynamics, mainly through longitudinal studies, to refine educational strategies that effectively address the diverse needs of ESP learners.