In 1944 - 1945 Rotta contributed greatly to the saving action of the Neutral Powers (Portugal, Spain, Sweden, Switzerland, the Vatican) and the International Red Cross Committee in Budapest (initiated by Carl Lutz, and led, among others, by Giorgio Perlasca, Friedrich Born, Raoul Wallenberg, Angel Sanz Briz). As the Dean of the Diplomatic Corps, he vehemently protested several times to the Hungarian Governments against the Jewish Deportations.
On 15 November 1944, the Hungarian Government established the "Big Ghetto" for 69,000 Jews, while a further 30,000 with protective documents went to the International Ghetto. On 19 November 1944, the Vatican joined the four other neutral powers - Sweden, Spain, Portugal and Switzerland - in a further collective protest to the Hungarian Government calling for the suspension of deportations of the Jews. The government complied, and banned the "death marches" - but Budapest was by that stage near anarchy, and deportations continued from 21 November. The Arrow Cross continued their orgy of violence, raiding the international Ghetto and murdering Jews, as Soviet forces approached the city. Rotta and Wallenberg were among the few diplomats to remain in Budapest. Following the Soviet conquest of the city, Wallenberg was seized by the Russians and taken to Moscow, from where he was never released. Gilbert wrote that of the hundred and fifty thousand Jews who had been in Budapest when the Germans arrived in March 1944, almost 120,000 survived to liberation - 69,000 from the Big Ghetto, 25,000 in the International Ghetto and a further 25,000 hiding out in Christian homes and religious institutes across the city.
Post-war.
Rotta retired from diplomacy in 1957.
Pope Paul VI paid him a surprise visit at his Vatican residence on Easter Sunday in March 1964.
He was recognized as Righteous among the Nations by Yad Vashem in 1997.