Pope Paul VI named Arns titular bishop of Respecta and auxiliary bishop of São Paulo on 2 May 1966. He was consecrated on 3 July 1966 by Cardinal Agnelo Rossi. The same pope appointed him Archbishop of São Paulo on 22 October 1970 and he was installed on 1 November. In 1973 he sold the episcopal palace, a mansion standing in its own park. Two things horrified him: the massive electricity bills and the staff of 25 sisters and brothers assigned to look after his needs. He used the money from the sale to build a social station in the favelas.