[3][6] He subsequently undertook postgraduate studies at the Pontifical University of Saint Thomas Aquinas in Rome, obtaining a Doctor of Sacred Theology degree in 1952.
He then became diocesan director of Catholic Action the following year, before serving as vice-chancellor of the Archdiocese of Saint Boniface and secretary to Maurice Baudoux.
[8] During his tenure as diocesan bishop, De Roo was known as a strong proponent of activism and liberation theology and was a critic of capitalism.
That document stated that the "goal of serving the human needs of all people in our society must take precedence over the maximization of profits and growth""[9] He also supported the ordination of women and married priests.
[3] His decision to broach the latter subject during a lunch with Pope John Paul II and other bishops in 1994 drew the ire of the pope, while his address to a conference in the US calling for a dialogue about the former resulted in De Roo being summoned to Rome in 1986 and reprimanded by Joseph Ratzinger, the prefect of the Congregation for the Doctrine of the Faith at the time.
[3][11] At around the time of his retirement, he intended to address an international convention of married Catholic priests in Atlanta.
Over a 15-year period, despite being a critic of capitalism he made a series of large investments in real estate and in a horse-breeding ranch without adhering to canonical requirements for consent from the Vatican, consultation with diocesan clergy, or financial record-keeping.
[16] De Roo was ultimately cleared of any wrongdoing by a jury in the civil action, which determined that he had actually made a sound investment.
He described attending the sessions as "a voyage of discovery that would radically alter my whole outlook on reality" and "it was indeed a time of euphoria".
[19] After 37 years of serving as Bishop of Victoria, De Roo reached the mandatory retirement age of 75 in February 1999.