Digitalisation and Human Capital (HC) are key drivers of economic transformation, yet their joint influence on environmental outcomes remains underexplored in developing economies. Existing evidence largely focuses on linear or isolated effects, overlooking potential nonlinearities and complementarities crucial for sustainable development. This study investigates the nonlinear and interactive impacts of digitalisation and HC on carbon emissions in 23 developing countries from 2000 to 2023. A multidimensional digitalisation index is constructed using Principal Component Analysis (PCA), integrating digital infrastructure, industrialisation, and innovation. Employing a dynamic system Generalised Method of Moments (GMM) estimator, the study captures endogeneity, persistence, and feedback mechanisms. Results confirm that both digitalisation and HC exhibit U-shaped relationships with carbon emissions. While early stages enhance efficiency and environmental awareness, advanced levels intensify emissions through energy-intensive infrastructure and industrial upgrading. The interaction between digitalisation and HC is insignificant, revealing unrealised synergies in developing contexts. The study contributes to the environmental economics literature by integrating digital and HC dynamics into a unified nonlinear framework and offers policy insights for aligning digital transformation with renewable energy deployment, green skill formation, and institutional coordination to advance low-carbon, human-centric growth.