With rapid industrialization and urbanization in China, cultivated land conversion (CLC) has posed a significant threat to food security. Understanding the spatiotemporal patterns and drivers of CLC is crucial for promoting sustainable land use and economic development. However, existing research on CLC driving mechanisms has notable limitations: temporal studies often neglect spatial heterogeneity, while spatiotemporal analyses struggle to establish clear causal relationships. Therefore, this study aims to elucidate the causal mechanisms of CLC from a spatiotemporal perspective. Using land use data from Guangdong Province (2001–2020), we identified CLC patterns and applied geographical convergent cross mapping to examine causality. Results show that CLC in Guangdong expanded until 2012, then sharply declined and stabilized. Spatially, changes were more intensive along the coast and milder inland. We found that CLC drivers vary across stages, but socioeconomic factors consistently dominate. GDP growth, population increase, and urbanization emerged as primary drivers. Physical geography also constrained CLC distribution, while cultivated land endowment showed no significant impact. These insights from a rapidly developing Chinese province provide valuable implications for global cultivated land conservation and sustainable development.