Towards the end of World War II, under the national socialist government of the Arrow Cross Party, he gave a speech in which he announced that he in no way opposed the actions of the fascist régime.

[6] In August 1950, in his position as archbishop, he signed an agreement with the Hungarian state in order to settle the fate of 2,000 imprisoned nuns and monks.

[8] As much of the Church continued to protest the violent oppression of religious activities,[5] Grősz was arrested in May 1951 and sentenced to 15 years imprisonment on charges of conspiring with the United States and the Vatican to overthrow the government.

[9] He was pardoned in 1956 alongside opposition politicians such as Zoltán Tildy, after supposedly promising to act as a "faithful son of the republic".

[10] Once released from prison, Grősz assumed the leadership of the Hungarian Bishops' Conference and, while serving in this position, was elected to the national council of the governing Popular People's Front.