Supriyadi was born in what is now Trenggalek, Dutch East Indies, on 13 April 1923. He attended junior high school, then a school to prepare him for government bureaucracy in Magelang. However, the Japanese invaded Indonesia before he graduated. He then switched to high school and underwent youth training (Seimendoyo) in Tangerang, West Java.[1]

In October 1943, the Japanese established a militia, PETA (Indonesian: Pembela Tanah Air, lit. 'Defenders of the Homeland') to assist Japanese forces against the Allies. Supriyadi joined PETA, and after training was posted to Blitar. He was tasked with overseeing the work of the Romusha forced laborers. The plight of these workers inspired him to rebel against the Japanese. When Supriyadi join with PETA, he was given the rank of shodancho or platoon commander. 

When nationalist leader Sukarno visited his parents in Blitar, PETA officers told him that they had begun to plan a rebellion and asked for Sukarno's opinion. He told them to consider the consequences, but Supriyadi, leader of the rebels, was convinced the uprising would succeed.

In the early hours of 14 February 1945, rebels attacked Japanese troops, causing heavy casualties. However, the Japanese defeated the rebellion and put the ringleaders on trial. Six (or eight[2]) people were sentenced to death and the rest were given jail sentences ranging from three years to life. However, Supriyadi reportedly was not executed. Some said Supriyadi escaped and hid from the Japanese.[1][3] He was not seen again after the failure of the rebellion.[4]