He was a confidant of Prime Minister Shigeru Yoshida and served as a liaison between Japanese cabinet and the Supreme Commander for the Allied Powers during the American occupation of Japan.

Jirō's paternal grandfather Taizō was a prominent samurai of the Sanda Domain who had supported the Meiji Restoration, later becoming a businessman and briefly president of the Yokohama Specie Bank.

By his own account, Shirasu was a troublemaker in his youth and him studying abroad had been arranged by his father as a form of "exile.

"[1][2] Shirasu enrolled in Clare College at Cambridge University in April 1923 and read medieval history.

During winter break in 1925 he made a tour of the European continent together with Byng in his Bentley, driving down to Gibraltar and back.

In December 1945, Shirasu was recruited by his friend Shigeru Yoshida, who had become foreign minister, to the Central Liaison Office.

After Yoshida had become prime minister, Shirasu was concurrently appointed deputy director-general of the Economic Stabilization Board in December 1946.

In the post-war era, his wife Masako Shirasu had become a collector and expert of fine Japanese art, on which she published a number of books.