Otani graduated from the Bungakuryo School.
In 1904, Otani was sent by the Jodo Shinshu to the Liaodong Peninsula, to minister to Japanese forces during the Russo-Japanese War.
In December 1905, he was ordered the Qing dynasty China to lay the foundations for a network of Jodo Shinshu temples and missionary activities. In September 1907, he made a tour through Southeast Asia before returning to Japan to assume his duties as an official at the Higashi Honganji in Kyoto.
He travelled to Korea in 1909 to assist in the development of a network of Jodo Shinshu temples, and departed for London in May 1910. However, due to the financial scandal which enveloped his brother, Otani Kozui, then 22nd head of the sect, he was forced to curtail his trip in July 1910. He became secretary-general of the sect in March 1921.
In October 1925, Otani left for a tour of the United States and Canada, returning to Japan at the end of February 1926. On April 4, 1928, he was appointed to a seat in the House of Peers.
On June 4, 1937, he was asked by Prime Minister Fumimaro Konoe to accept the post of Minister of Colonial Affairs, which he held to May 26, 1938. In November 1938, he assumed the post of Director of the North China Development Company, a subsidiary of the South Manchuria Railway dedicated to the economic development of the areas of northern China under occupation by Japan. From July 1939, he was also a member of the East Asia Development Board.
Otani was a son of Otani Koson, the 21st hereditary head of the Jodo Shinshū branch of Japanese Buddhism.
His brother, Otani Kozui was the 22nd head of the sect, and a noted explorer of Central Asia, while his sister was Takeko Kujo, a noted poet and humanitarian.