He entered the Congregation of the Missionary Sons of the Immaculate Heart of Mary (Claretians) and made his religious profession on 8 September 1946.

After completing his studies in philosophy and theology in the seminaries of the congregation, he was ordained a priest on 28 June 1953.

[1] Sebastián Aguilar obtained a doctorate in Sacred Theology from the Pontifical University of St. Thomas Aquinas, Angelicum in 1957 with a dissertation entitled “Maternitatis divinae diversa ratio apud Didacum Alvarez et Franciscum Suarez”.

[2] He became a member of the Sociedad Mariológica Española in 1959 and served as director of the Revista Ephemerides Mariologicae in 1966.

Pope Francis announced on 12 January 2014 that on 22 February, Archbishop Sebastián Aguilar, along with 18 other individuals, would be inducted into the College of Cardinals.