With the rapid socioeconomic development of China, studies related to Internet use and civil servants’ happiness have become a research hotspot in Chinese academia. This study empirically analysed the impact of Internet use on the happiness of Chinese civil servants using a sample of 3793 civil servants in Hunan Province, China. It showed that Internet use significantly enhanced the subjective well-being of Chinese civil servants. Furthermore, heterogeneity analysis revealed significant heterogeneity in the effect of the Internet on civil servants’ happiness, which varied across civil service groups with different education and gender. Moreover, the effect of Internet use on the happiness of the male and better educated civil servant groups was more pronounced than in the female and less educated civil servant groups. Additionally, mediation analysis revealed that Internet use and the happiness of civil servants were not linear, with health having a significant mediating effect. This indicates that Internet use helps civil servants maintain good health, and thereby enhances the happiness of civil servants. In addition, we also use a propensity score matching model (PSM) to address the endogeneity problem due to sample selectivity bias. The results show that the estimates are more robust after eliminating sample selectivity bias. The effect of Internet use on civil servants’ subjective well-being would be underestimated if the sample selectivity bias is not removed.