The Legion of Mary was founded in Dublin by Frank Duff, a civil servant, driven by a vision to enable lay people to engage in the apostolate and contribute meaningfully to the Church's mission. Established as a response to the significant spiritual needs of the era, which saw a decline in religious practice among laypeople, Duff envisioned an organization that would empower the laity. Its first meeting took place in a modest hall, and it initially attracted only a handful of volunteers, but the enthusiasm and commitment from its members quickly led to its expansion.

Recruiting all those eager to serve, the Legion of Mary set out to undertake various spiritual works, including visiting the sick, teaching catechism, and engaging in parish activities. This community-driven approach fostered a deep sense of belonging and mission among its members. As they spread throughout Ireland, the Legion became instrumental in revitalizing parish life and encouraging Catholic engagement at a grassroots level. Today, it stands as the largest lay organization in the Catholic Church, with millions of members worldwide dedicated to various forms of service.

The impact of this organization extends beyond its immediate spiritual activities; it's not only influenced church practices but also inspired similar initiatives globally. The Legion of Mary has nurtured a culture of volunteering within the Church, demonstrating how laypeople can fulfill vital roles in ecclesiastical missions. This initiative ultimately shaped the future of lay engagement in the Church.