This article attempts to investigate the public defender office’s intervention in Brazilian’s civil litigation as custos vulnerabilis. It will analyze whether this legal construction effectively has a redistributive impact on law and changes the status quo or would it be a symbolic commitment. It uses the argumentative dialectical approach method; the structuralism procedure method and the sociological interpretation method. As a research hypothesis, it considers that public defender office’s intervention as a “vulnerable’s guardian” is legitimated by the protection of vulnerable group’s fundamental rights. The objectives of this essay are: i) to analyze the public defender’s intervention as custos vulnerabilis; ii) to examine the civil litigation neutrality discourse and the limitations to law’s transformation by Marc Galanter; iii) associating law and culture, to investigate whether the referred intervention modality has the aptitude to promote social change, analyzing its theoretical basis of legitimation. The conclusions show that: i) the public defender office’s intervention as custos vulnerabilis is interpreted from art. 134 of Brazilian’s Constitution, to promote fundamental human rights; ii) the recognition of this interventional modality by jurisprudence reveals the Brazilian society’s cultural transformation and of process itself; iii) this interventional modality’s consolidation may contribute to a paradigm shift in Brazilian civil process, making it more inclusive and fairer.