Kentaro Ochiai graduated from Law Department, Tokyo University (1895).
Joined the diplomatic service and served in the consulates at Seoul and Kia Chow. At the Portsmouth Peace Conference following the Russo-Japanese War (1905), he was chief secretary of the Japanese delegation. He was subsequently counselor at the embassy in Russia and consul general in Mukden. Was appointed ambassador to Italy (1920) and chief delegate to the Lausanne Conference (1923).