Based on a sample of A-share companies listed on the Shanghai Stock Exchange and the Shenzhen Stock Exchange from 2011 to 2022, this paper measures and analyzes the degree of enterprises’ digital–green synergy and further tests the influence mechanism of fintech on enterprises’ digital–green synergistic development. It is found that fintech has a significant positive effect on enterprises’ digitization, enterprises’ greening, and their digital–green synergistic development, and the conclusion still holds after robustness and endogeneity tests. A heterogeneity analysis shows that the heterogeneity of enterprises’ size and the degree of industry emissions affects the promotional effect of fintech on the synergy. Fintech effectively promotes enterprises’ digital–green synergistic development through the three channels of green innovation, efficiency enhancement, and environmental information disclosure, and the heterogeneity of the executive team’s ages and the heterogeneity of their occupational backgrounds have a positive moderating effect on the promotional effect of fintech. The findings provide a conceptual framework and policy formulation guidelines for fintech to support the promotion of enterprises’ digital–green synergy and the improvement of new-quality productivity.