Piacenza taught canon law at the Theological Faculty of Northern Italy and held several other posts, serving as the archbishop's press officer.

[2] On 13 October 2003, Pope John Paul II appointed Piacenza President of the Pontifical Commission for the Cultural Heritage of the Church and titular bishop of Victoriana.

[5] That appointment has been interpreted as Pope Benedict's way of positioning a thoroughly orthodox secretary to monitor the work of his superior, the far more liberal Cardinal Claudio Hummes.

Pope Francis reappointed them temporarily[11] and then moved Piacenza from his position as Prefect of the Congregation for the Clergy to head the Apostolic Penitentiary on 21 September 2013.

[12] His new role was described as "a decidedly lower command post" as head of "a little-known Vatican tribunal that deals with confessions of sins so grave only a pope can grant faculties to absolve from them, such as the case of a priest who violates confessional secrecy".