Abstract This study aims to analyze the role of Tax Volunteers in mediating the influence of the e-filing system and tax knowledge on the compliance of individual taxpayers in Deli Serdang Regency. The background of this study is based on the low level of taxpayer compliance in Indonesia, despite the modernization of tax administration through the e-filing system and various efforts to improve tax literacy through the Tax Volunteer program. This study uses a quantitative approach with the Partial Least Squares – Structural Equation Modeling (SEM-PLS) method processed using SmartPLS version 4.0. The research population consists of individual taxpayers registered at the Lubuk Pakam Tax Office (KPP) who have interacted with Tax Volunteers. The sampling technique used purposive sampling with a total of 100 taxpayer respondents. Data were collected through the distribution of questionnaires using a 1–5 Likert scale and analyzed through outer model testing (validity and reliability) and inner model testing (hypothesis testing and mediation testing). The results of the study show that: (1) The e-filing system has a positive and significant effect on taxpayer compliance with a coefficient value of 0.351 and a p-value of 0.000; (2) Tax knowledge has a positive and significant effect on taxpayer compliance with a coefficient of 0.194 and a p-value of 0.010; (3) Tax volunteers partially mediate the effect of the e-filing system on taxpayer compliance with an indirect effect value of 0.087 and a p-value of 0.007; and (4) Tax volunteers partially mediate the effect of tax knowledge on taxpayer compliance with an indirect effect value of 0.398 and a p-value of 0.000. These findings indicate that the presence of Tax Volunteers can strengthen the influence of the e-filing system and tax knowledge on taxpayer compliance. Thus, the synergy between digital taxation transformation, increased tax literacy, and social participation through Tax Volunteers has proven effective in improving sustainable tax compliance.