Olney Sr. co-founded the Sierra Club in his law office with naturalist John Muir, and others, but was later expelled from the organization because he supported the flooding of Hetch Hetchy Valley to supply water to San Francisco.

[13] Beginning July 1, 1932, he served as president of the alumni association for two years, and thus sat as a regent.

[14][13] Olney was appointed Associate Justice of the California Supreme Court by Governor William Stephens, and served from March 1919 to July 1921.

[17] In 1930 to 1932, he was a special assistant to the Attorney General of the United States in antitrust litigation concerning the Radio Corporation of America.

[4] The youngest son, Warren Olney III (February 25, 1904 – December 23, 1978), became an attorney and practiced in his father's law firm.

[4] He was appointed by President Dwight D. Eisenhower as an Assistant Attorney General to oversee the Criminal Division of the United States Department of Justice.