This study explores how cross-curricular lesson planning influences pre-service teachers' understanding of sustainable development (SD) and their engagement with education for sustainable development (ESD). Based on pre-service teachers' experiences and insights, the study aims to contribute to a more holistic approach to integrating SD into ESD practices, ultimately preparing future educators to effectively address sustainability challenges across various subject areas. This study employed a mixed-methods case study design to investigate the influence of cross-curricular lesson planning on pre-service teachers' holistic understanding of SD and their capacity to implement ESD principles. The investigation was carried out at a state university in Türkiye, with the participation of 35 pre-service teachers from different subject areas. The findings revealed that cross-curricular lesson planning significantly enhances pre-service teachers' holistic understanding of SD while fostering the interdisciplinary teaching strategies essential for ESD. The collaborative nature of this approach broadens their perspectives on sustainability issues and strengthens their ability to integrate SD concepts across disciplines, supporting the complex, interconnected nature of ESD. This study highlights the potential of cross-curricular collaboration in teacher education to prepare future educators for effective ESD implementation, offering valuable insights into how such pedagogical strategies can enhance sustainability-oriented teaching and learning.