Yoshizumi was born in Oizumi-mura, Nishitagawa District, Yamagata, on 9 February 1911. He studied in Tsuruoka. He first went to the Dutch East Indies in 1932, where he worked at a brothel to recruit native Javanese officials as Japanese agents. Outside of Java, Yoshizumi also networked with Minahasan people of Sulawesi. His early contributions to journalism included working as reporter for the Nichiran Shōgyō Shinbun, which employed him in 1935. Later, Yoshizumi was tasked with becoming a spy in Dutch East Indies by posing as a worker in Toko San'yo, a Japanese shop. He later founded Tōindo Nippō, a newspaper which combined Nichiran Shōgyō Shinbun and Jawa Nippō, in order to unite Japanese people in the Dutch East Indies. Although working for the Imperial Japanese Navy, Yoshizumi was not a career member, and was instead an attached civilian promoted to an officer. 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. He returned clandestinely and was arrested again in December 1941, when war broke out between the Netherlands and Japan. He was detained in January 1942 and sent to a detainee camp in Loveday, South Australia. During his stay there, the East Indies were conquered by Japan and placed under a military regime. Yoshizumi was finally repatriated in August, following a prisoner exchange. During 1945, while serving as a chief of the Kaigun Bukanfu under Admiral Tadashi Maeda, Yoshizumi secretly aligned with Indonesian nationalism. According to statements by his friend, Shigetada Nishijima, he had actually adopted Marxism, having previously been a supporter of right-wing Japanese nationalism. 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. Later, he would help to compose the text of the proclamation itself. Yoshizumi met Tan Malaka in Achmad Soebardjo's house shortly after the proclamation. He then deserted his post and aligned with Indonesia when he joined with Tan Malaka's group, where he was called Arif. He arrived there with stolen Japanese Navy resources, which went into funding Tan Malaka's guerilla movement. During the uprising, Yoshizumi was largely involved with independence movements in East Java. He died from lung problems as a guerilla fighter at a mountain near Blitar on 10 August 1948. He was buried at the Taman Makam Pahlawan of that city. Yoshizumi's story was recounted in a book by historian Wenri Wanhar, titled Jejak intel Jepang: kisah pembelotan Tomegoro Yoshizumi. Following his death, during a 1958 visit to Japan, Sukarno delivered a letter to Shigetada Nishijima as a tribute for Yoshizumi and Ichiki Tatsuo. A small monument was then erected at Seisho-ji temple of Minato, Tokyo, with the following inscription:
