Cardijn played a role at Vatican II from the beginning of the Council as a participant in the Commission on laity.
Once appointed as a bishop and cardinal in 1965 he became a Council Father and played a more direct role in the lobbying process that led to the drafting of the later Vatican II documents.
Cardijn with Pat Keegan and Bartolo Perez, both former IYCW presidents and lay auditors at Vatican II
Cardijn was made a bishop and cardinal by Pope Paul VI at the beginning of 1965. He was thus able to participate as a Council father in the fourth and final session of the Second Vatican Council at the end of that year.