Keijiro Okano graduated from the Law Department of Tokyo University (1886) and went to Germany for study (1891), studied commercial law.
Keijiro Okano was appointed professor of his alma mater (1895) after returning to Japan.
He worked as a bureaucrat at various cabinet ministries in the Meiji government, and was appointed to a seat in the Upper House of the Diet of Japan in 1908. Keijiro Okano served as Director-General of the Cabinet Legislation Bureau under the 1st and 2nd Saionji administration (1906–1908; 1911–1912), and the 1st Yamamoto administration (1913). From 1913 to 1922, Okano served as Secretary to the Administrative Court.
In 1922, Okano was appointed Minister of Justice in the cabinet of Prime Minister Kato Tomosaburo. In the subsequent 2nd Yamamoto Gonnohyoe administration, he held the portfolios for Minister of Education and Minister of Agriculture and Commerce. In October 1925, Okano was appointed to Vice-President of the Privy Council. He was also appointed President of the prestigious Imperial Academy.