This article examined the significance of the Legion of Mary's participation in parish life as a representation of lay apostolate within the Catholic Church. The aim was to elucidate the Legion of Mary's role in carrying out the five duties of the Church. The content was derived from experiences gained while accompanying the Presidium of Mary, the Mother of the Church in Christ the King Parish, Surabaya. A qualitative research approach was employed in this study. The findings demonstrated that the Legion of Mary, as a Catholic group, instilled valuable principles in its members or Legionaries, emphasizing self-purification through acts of service driven by the needs and circumstances within the praesidium. The active involvement of the Legion of Mary members in parish life served as a tangible expression of the lay apostolate. Based on the study's findings, it can be concluded that members of the Legion of Mary contributed to implementing the Church's five duties, thereby supporting and enriching the lives of the parish community. The Legion of Mary's participation in parish life played a significant role in fostering a sense of community and strengthening the faith of its members. This study sheds light on the importance of lay apostolate and the contributions of Catholic groups like the Legion of Mary in fulfilling the Church's mission within the parish context.