Van Roey then furthered his studies at the University of Louvain, from where he obtained his doctorate in theology and the habilitation in 1903. He taught at the "Collège Americaine" from 1901 to 1905, and at the University of Louvain from 1905 to 1907. During this time, Van Roey also became a friend of Columba Marmion, OSB, who would later be beatified in 2000. On 19 May 1907, he was made an honorary canon of the metropolitan chapter of Mechelen. He served as vicar general of the city from 30 September 1907 to 1925, and was raised to the rank of Domestic Prelate of His Holiness on 2 April 1909. Van Roey participated in the Conversations of Mechelen, a series of ecumenical dialogues between clergymen from the Roman Catholic and Anglican Churches hosted by Cardinal Désiré-Joseph Mercier, from 1921 to 1926, but for which he was less supportive. He became secretary of the diocesan synod in 1924, and a protonotary apostolic on 11 February 1925.