She was born on Staten Island, on July 8, 1862, and grew up in Bridgeton, New Jersey. She was married first to Lucien Ware, then Louis Cohen, and finally Andrew Omholt. After marrying Lucian Ware when she was nineteen, she was a mother of four by 1892. Her son, Harold Ware, founded the Washington, D.C. based "Ware group" of United States federal government employees who spied for the Soviet Union in the 1930s and 1940s. One of her other sons was Buzz Ware, an artist and prominent leader in the Village of Arden, Delaware, where she lived for many years.
Bloor became involved in several reform movements including the prohibitionist Women's Christian Temperance Union (WCTU) and women's suffrage and wrote two books, Three Little Lovers of Nature (1895) and Talks About Authors and Their Work (1899).
In 1897 she joined with Eugene V. Debs and Victor Berger to form the Social Democratic Party (SDP). The following year she moved to the more radical Socialist Labor Party that was led by Daniel De Leon. However, in 1902 she became a member of the Socialist Party of America (SPA).
Bloor worked as a trade union organizer and helped during industrial disputes in Pennsylvania, Michigan, Colorado, Ohio and New York. In 1905 she helped a fellow member of the Socialist Party of America, the author, Upton Sinclair, to gather information on the Chicago stock yards. This material eventually appeared in Sinclair's best-selling book, The Jungle.
A leading figure in the Socialist Party of America, she ran several times unsuccessfully for political office, including secretary of state for Connecticut, Governor of Pennsylvania, and lieutenant governor of New York.
Bloor, a member of the left-wing faction of the Socialist Party of America, was expelled from the party in 1919. Bloor joined with others ousted from the SPA to form the Communist Party USA. In 1921 and 1922 attended the second conventions of the Comintern in Moscow and was a member of the party's central committee (1932-48).
After the German invasion of the Soviet Union in June 1941, Bloor became an advocate of American participation in World War II. Later she argued for an early invasion of Europe to create a Second Front.
Ella Reeve Bloor's autobiography, We Are Many, was published in 1940, and is the basis for the Woody Guthrie song, 1913 Massacre. She died in Richlandtown, Pennsylvania on 10 August 1951, and is buried in Harleigh Cemetery, Camden, New Jersey.