Minobe was born in Tokyo's Hongō Ward. His father, Tatsukichi Minobe, was a noted constitutional scholar, while his mother Tamiko was the eldest daughter of mathematician, educator, and politician Dairoku Kikuchi. He was the great-great-grandson of Edo Period samurai Mitsukuri Genpo.

He graduated from the law faculty of Tokyo Imperial University in 1927 and lectured in the agriculture faculty from 1929 to 1932. In 1935, he took a faculty position at Hosei University.

Minobe was arrested in 1938 due to suspicions of Communist Party ties, and spent 18 months in Sugamo Prison. After his release, he worked as a farmer.^[1]

In 1945, Minobe became an editorial writer for the newspaper Mainichi Shimbun. He was chosen to head the Cabinet Statistics Office in 1946.

Minobe entered the national spotlight in 1960 as the host of a program on NHK where he explained economics for general audiences.^[2]

Japan saw a wave of socialist and communist success in local elections starting in the early 1960s, when protests against the security treaties with the United States galvanized the left wing. In 1965, the Tokyo metropolitan government was embroiled in a major bribery scandal and a massive infestation of flies occurred due to garbage dumping at Yumenoshima, leading to a tumultuous metropolitan assembly election that resulted in the socialist wing taking control.^[2]

In 1967, incumbent conservative governor Ryotaro Azuma declined to run for re-election, and Minobe ran as the Communist and Socialist candidate for Governor of Tokyo. He defeated his two rivals, Rikkyo University president Masatoshi Matsushita (nominee of the LDP and DSP) and Shibusawa Shipping head Ken'ichi Abe (nominee of Komeito).

Among his many policy achievements, he is best known for:

• providing free health care for the elderly
• enactment of pollution controls^[3]
• converting streets in heavily trafficked areas to pedestrian-only use^[3]
• allowing the construction of the Korean School in Tokyo and exempting its owner, Chongryon, from local taxation^[4]
• ending government sponsorship of Korakuen Hall race tracks^[3]

In 1971, Minobe won re-election, defeating LDP candidate Akira Hatano. He was re-elected for a third term in 1975, with the backing of the Socialists, Communists, and Komeito. (His defeated rival, LDP candidate Shintarō Ishihara, later served as a cabinet minister and eventually won the Tokyo governorship in the 1999 election.)

The LDP-controlled national government under Kakuei Tanaka mimicked some of Minobe's socialist policies in Tokyo, including free health care for the elderly and for children with cancer, in an attempt to ride the public popularity of these programs.^[3]

Japan's left wing lost popularity in the 1970s due to the 1973 oil crisis, growing criticism of welfare programs, and difficulty in completing public works projects. Minobe was narrowly re-elected in 1975, but his coalition lost control of the Tokyo metropolitan assembly in 1977.^[3]

Many of Minobe's policies toward Chongryon, the Zainichi Korean group affiliated with North Korea were later undone by Ishihara in the aftermath of the revelation of North Korean abductions of Japanese.^[4]

Minobe refused to run for a fourth term in 1979. He ran for the House of Councillors in 1980 and won a seat. He remained a member of the Diet until his death of a heart attack in 1984.^[1]