Equity and efficiency are two important factors guiding the mitigation of anthropogenic emissions to achieve the Paris climate goals. Previous studies have proposed a range of allocations of global carbon budgets, but few have quantified the equity–efficiency interaction. Based on an investigation of the existing allocation literature, this study conducts a novel analysis using a ‘mixed’ allocation ‘big-data’ framework to understand the equity–efficiency interaction in the distribution of global carbon budgets under 2 °C and 1.5 °C warming targets. At a global scale, a carbon Gini coefficient and aggregate abatement costs are used as quantitative metrics to reflect equity and efficiency, respectively. Results show an equity–efficiency frontier that reflects the opportunity for the international community to co-improve equity and efficiency on top of existing allocations. However, the frontier also features strong trade-offs to further improve equity and efficiency if national allocations are to be achieved individually. Our analysis verifies that such trade-offs are sensitively dependent on the level of global connection and integration. Linking national mitigation actions and potentials can help promote equity–efficiency synergies and contribute to the efficient achievement of the Paris Agreement's temperature and equity goals.