He then fulfilled pastoral assignments in Buenos Aires for several years and in 1975 began teaching on law at the Pontifical Catholic University of Argentina.
On 22 July 1993, Pope John Paul II appointed him Auxiliary Bishop of Buenos Aires with the titular see of Theuzi.
[2] On 19 May 2014, Pope Francis assigned Mollaghan to the Congregation for the Doctrine of the Faith in Rome to work on a commission responsible for handling cases of clerical pedophilia.
[2] The seven-member Commission was established on 11 November 2014 with responsibility for sexual abuse of minors, heresy, apostasy, misuse of the sacrament of penance, and the ordination of women.
[4] Mollaghan denied that he represented a more conservative faction of the Argentine hierarchy and pointed to his long service alongside Bergoglio in Buenos Aires.