William Patterson was born in San Francisco on 27th August, 1891. His mother had been a slave and spent her childhood on a Virginia plantation.
While studying at the University of California he began reading The Crisis, The Masses and The Messenger. After graduating with a law degree in 1919 he joined the National Association for the Advancement of Coloured People (NAACP) where he met his future wife, Louise Thompson.
Patterson spent time in London where he met George Lansbury and other leading figures in the Labour Party. He also contributed articles to the socialist newspaper, The Daily Herald on the problems faced by black people in the United States. Patterson intended to move to Africa but Lansbury convinced him to return to the United States.
Patterson met Paul Robeson in 1920. The two men became very active in left-wing politics. Patterson also became friends with Heywood Broun who tried to persuade Patterson to join the Socialist Party. Patterson rejected the idea and eventually became a member of the American Communist Party, Patterson was a regular contributor to the Daily Worker. Patterson was also a regular contributor to the Daily Worker.
In 1923 Patterson and two friends opened a law office in Harlem. As a lawyer, Patterson was involved in several campaigns to free people wrongly convicted of criminal acts. This included the defence of Nicola Sacco and Bartolomeo Vanzetti, two anarchists who were eventually executed in August, 1927. Patterson also worked on the Scottsboro Case, where nine young black men were falsely charged with the rape of two white women on a train.
Patterson went to the Soviet Union in 1927 and enrolled in the Far East University and took part in the Sixth Comintern Congress in Moscow. In 1930 Patterson was a delegate to the World Conference Against Racism and Anti-Semitism in Paris, France.
After arriving back in the United States Patterson returned to his law practice in Harlem. Patterson was also executive secretary of the International Labor Defense and leader of the Civil Rights Congress.
In 1951 Patterson joined with Paul Robeson, Eslanda Goode, Harry Haywood, Mary Church Terrell, Robert Treuhaft, Jessica Mitford, Louise Thompson to deliver a petition to the United Nations which charged the United States government with genocide. The petition was a detailed documentation of hundreds of cases of murder, bombing, torture of black people in the United States. It provided details of the "mass murder on the score of race that had been sanctified by law" and stated that "never have so many individuals been so ruthlessly destroyed amid so many tributes to the sacredness of the individual".
Patterson was also involved in the defence of Angela Davis and Black Panthers leaders arrested during the 1960s. His book The Man Who Cried Genocide, was published in 1971. William Patterson died in 1980.