Educated at Packer Collegiate Institute and Radcliffe College, Ovington became involved in the campaign for civil rights in 1890 after hearing Frederick Douglass speak in a Brooklyn church. She later wrote: "I had never seen Frederick Douglass before and I was never to see him again, but that night was to me a great event. I had come face to face with one of my heroes. He was one of the great group of men and women who had risked all for freedom."
In 1895 she helped found the Greenpoint Settlement in Brooklyn. Ovington met Jane Addams, the founder of Hull House, soon afterwards. Ovington remembers Addams telling her: "If you want to be surrounded by second-rate ability, you will dominate your settlement. If you want the best ability, you must allow great liberty of action among your residents."
Appointed head of the Greenpoint Settlement the following year, Ovington remained until 1904 when she was appointed fellow of the Greenwich House Committee on Social Investigations. Over the next five years she studied employment and housing problems in black Manhattan. During her investigations she met William Du Bois, an African American from Harvard University, and she was introduced to the founding members of the Niagara Movement.
Influenced by the ideas of William Morris, Ovington joined the Socialist Party in 1905, where she met people such as Daniel De Leon, Asa Philip Randolph, Floyd Dell, Max Eastman and Jack London, who argued that racial problems were as much a matter of class as of race. Ovington wrote for radical journals and newspapers such as, The Masses, New York Evening Post and The Call. She also worked with Ray Stannard Baker and influenced the content of his book, Following the Color Line (1908).
In September 1908 Ovington read an article by William English Walling, entitled Race War in the North, that described the atrocities being carried out against African-Americans. Walling ended the article by calling for a powerful body of citizens to come to their aid.
Ovington responded to the article by writing to Walling and at a meeting in New York they decided to form the National Association for the Advancement of Coloured People (NAACP). The first meeting of the organization was held on 12th February, 1909. Early members included Josephine Ruffin, Mary Talbert, Mary Church Terrell, Inez Milholland, Jane Addams, George Henry White, William Du Bois, Charles Edward Russell, John Dewey, Charles Darrow, Lincoln Steffens, Ray Stannard Baker, Fanny Garrison Villard, Oswald Garrison Villard and Ida Wells-Barnett.
In 1910 Ovington was appointed as executive secretary of the NAACP. The following year she attended the Universal Races Congress in London. Ovington remained active in the struggle for women's suffrage and as a pacifist opposed America's involvement in the First World War. During the war Ovington supported Asa Philip Randolph and his magazine, The Messenger, which campaigned for black civil rights.
After the war Ovington served the National Association for the Advancement of Coloured People as board member, executive secretary and chairman. The NAACP fought a long legal battle against segregation and racial discrimination in housing, education, employment, voting and transportation. They appealed to the Supreme Court to rule that several laws passed by southern states were unconstitutional and won three important judgments between 1915-23 concerning voting rights and housing.
The NAACP was criticised by some members of the African American community. Booker T. Washington opposed the group because it proposed an outspoken condemnation of racist policies in contrast to his policy of quiet diplomacy behind the scenes. Members of the organization were physically attacked by white racists. John R. Shillady, executive secretary of the NAACP was badly beaten up when he visited Austin, Texas in 1919.
Ovington wrote several books and articles including a study of black Manhattan, Half a Man: The Status of the Negro (1911), Status of the Negro in the United States (1913), Socialism and the Feminist Movement (1914), an anthology for black children, The Upward Path (1919), biographical sketches of prominent African Americans, Portraits in Color (1927), an autobiography, Reminiscences (1932) and a history of the NAACP entitled, Walls Come Tumbling Down (1947).
Ovington who retired as a board member of the National Association for the Advancement of Coloured People in 1947 and in doing so, ended her thirty-eight years service with the organisation.
Mary White Ovington died in 1951.