He is one of two cardinals – along with Juan Luis Cipriani Thorne – who belong to Opus Dei; Herranz Casado is the organisation's highest-ranking member in the Church's hierarchy.

He is also considered one of the foremost experts in canon law, and to have been one of the Vatican's most influential figures during the period shortly before the death of Pope John Paul II.

Born in Baena in the Province of Córdoba, Herranz Casado joined Opus Dei in 1949 after reading a conspiratorial story about it as editor of a university newspaper.

[3] Herranz Casado received his episcopal consecration on 6 January 1991 from John Paul II, with Archbishops Giovanni Battista Re and Justin Francis Rigali serving as co-consecrators, in St. Peter's Basilica.

[9] In March 2012 Pope Benedict XVI established a Commission of Cardinals to investigate leaks of reserved and confidential documents on television, in newspapers, and in other communications media (in what is known as the Vatileaks scandal).