After joining Matsushita Electric Industrial Company (now Panasonic), Katsuhiko Eguchi was transferred to the Peace and Hope through Prosperity (PHP) Institute, a civilian policy think tank established by Kōnosuke Matsushita, the founder of Matsushita Electric. Eguchi worked at PHP while also serving as Matsushita’s personal secretary. He was the president of PHP from 2004 to 2009. After retiring from PHP, he ran in the 2010 House of Councillors election at the request of Watanabe Yoshimi of the Your Party (みんなの党). During the election, he called for the establishment of an “autonomous local dōshū system.” Eguchi was successful and was elected to the House of Councillors.
In 2012, Eguchi published the “Eguchi Draft” of the Constitution, a revised version of the current Constitution. In addition to the “autonomous local dōshū system”—which he had promoted in the past— Eguchi’s draft also contains a clause stipulating the Emperor is the head of state, and another related to the prime minister’s authority to command and supervise the Self-Defense Army (Jieigun). The “autonomous local dōshū system” decentralizes Japan’s government by giving administrative power to local governments. It is a form of government that aims to move away from the overconcentration of prosperous development in Tokyo by creating numerous strong economic areas throughout Japan.
In 2014, Eguchi participated in the Association for an Autonomous Constitution (自主憲法研究会) founded by Shintarō Ishihara and Takeo Hiranuma. He retired from the world of politics after the end of his term in 2016. After leaving the Minna no Tō, he became a member of the Jisedai no Tō (Party for Future Generations), and later the Osaka Ishin no Kai. In 2006, he became an adviser to the Chiiki Seitō Jiyū Jiyū o Mamoru Kai.