Born in Tōhoku region during the late stages of the Meiji period, in his early twenties he joined the Japanese expatriate community in the Dutch East Indies.

He spent time in an Australian internment camp, but was released during a prisoner exchange in August 1942, and returned to the East Indies, which were by then under Japanese occupation.

He ensured that Sukarno and Muhammad Hatta signed their names to the Proclamation of Indonesian Independence, which he also helped write.

Yoshizumi then joined Tan Malaka's network of anti-Dutch guerrillas, taking part as a soldier in the clashes of East Java.

Later, Yoshizumi was tasked with becoming a spy in Dutch East Indies by posing as a worker in Toko San'yo, a Japanese shop.

[5] Following the outbreak of World War II, Yoshizumi publicly advocated a "campaign for the new order in East Asia", which caused him to be deported.

According to statements by his friend, Shigetada Nishijima, he had actually adopted Marxism, having previously been a supporter of right-wing Japanese nationalism.

[4] On 16 August 1945, prominent nationalist leaders Sukarno and Muhammad Hatta were kidnapped and brought to Rengasdengklok, Karawang by some other figures in the movement to be convinced to declare Indonesian independence, and afterwards Yoshizumi was sent to accompany them back, to ensure that the military would not interfere.

[9] Following his death, during a 1958 visit to Japan, Sukarno delivered a letter to Shigetada Nishijima as a tribute for Yoshizumi and Ichiki Tatsuo (another Japanese who defected to Indonesia).