He graduated from Law Department of Meiji University in 1926.
Ken-ichi Shimomura became president (1930) and then auditor (1937) of Shimomura Steamship Company. He was appointed director of Taiyo Marine Transportation Company (1941). When the former company was amalgamated into the latter he was appointed its president (1943).
He held additional posts of director of Japan Shipowners' Association, Nihon Kaiun Shukaijo (Japan Marine Transportation Council), Nihon Senshu Sogo Sekinin Hoken Kumiai (Japan Shipowners' Mutual Responsibility Insurance Company) and director of Kobe Chamber of Commerce & Industry. Books include Jun Senjika-no Kaiun Gensei (The Actual Conditions of Marine Transportation Under the Quasi-Wartime Period) and Gendai Kaiunron (On Modern Marine Transportation).