Kate Richards was born March 26, 1876, to Andrew and Lucy Richards, farmers in Central Kansas. A drought in 1887, combined with the cumulative effects of the economic depression of the 1870s, completely devastated the family. Forced off their farm, the family moved to a poverty stricken area of Kansas City, where Andrew Richards barely made enough money for the family to survive.

In 1894, Kate found work as a machinist in a small Kansas City machine shop. During this year, she also met prominent socialist Mother Jones, who introduced her to Kansas City socialists and gave her books regarding socialism. This was followed in 1895 by a meeting with Eugene V. Debs, another noted socialist. In 1899, she and her father founded the Socialist Labor Party, although she later left the organization. In 1901, she was a founding member of the Socialist Party in America; she also met her future husband, Frank P. O'Hare, an Iowa born socialist from St. Louis. They were wed in January 1902, and then set out on a national lecturing and organizing tour. They eventually moved to Oklahoma in 1904, and operated a small farm there until 1908, when the family moved back to Kansas City with their four young children.

During her years in Kansas City, O'Hare remained a vocal and active supporter of socialism. She toured many southwestern states, often for the length of an entire summer. Her popularity was said to be second only to Eugene Debs himself. She also became a militant supporter of women's suffrage. She served as grand marshal for a suffrage parade in Washington, D.C. in 1913. Both in 1910 and in 1916, she ran for political office, even though women did not have the right to vote.

Kate Richards O'Hare was strongly opposed to United States entry into World War I. She toured throughout the nation, presenting a speech entitled "Socialism and the War." On July 17, 1917, she addressed a crowd in Bowman, North Dakota. The Bowman speech was the 76th time she had given the address. This time, however, she was arrested under the auspices of the 1917 Espionage Act. She was tried and convicted before a court in Bismarck, North Dakota, and was sentenced to five years in prison, to begin on April 15, 1919. In May 1920, her sentence was commuted and she was set free.

She remained active in her post-prison years. She led a march to Washington D.C. in 1922 to protest the treatment of opponents of the war, helped to organize a socialist college in Arkansas in 1925 and was active in Upton Sinclair's "End Poverty in California" campaign in 1928. She was especially active in the area of prison reform. She made her greatest contribution to that field in the state of California, where she was appointed Director of Penology. She directed many reforms of that state's penal system.

Kate Francis O'Hare died January 12, 1948, at the age of 71.