Born in Mainz, Germany, he became a socialist in his youth joining the Social Democratic Party but was expelled in 1890 for his support of the left wing group Die Jungen (The Young). His political views would soon move towards anarchism.
As a bookbinder by trade, he worked as a travelling journeyman for several years. His travels would bring him to many parts of Western Europe, observing the second congress of the Second International in Brussels in 1891. Rocker began contributing to the anarchist press in 1892 and left Germany the same year to escape police harassment, settling in Britain in 1895.
Rocker, a Gentile, became deeply involved in the Jewish anarchist movement while living in London, the Jewish anarchist movement being larger than the native anarchist movement in England. Learning Yiddish, then quickly becoming a prominent speaker and writer in the movement, Rocker became the editor for several Jewish newspapers, including Dos Fraye Vort (The Free Word), Der Arbeiter Fraint (The Workers' Friend) and Germinal. 1902, a federation of Jewish anarchist groups was formed, Rocker represented the federation at the International Anarchist Congress in Amsterdam in 1907.
Rocker was interned as an enemy alien during the First World War and Arbeiter Fraint was suppressed. The Jewish anarchist movement in Britain never fully recoverd from these blows.
In 1918 Rocker was deported from Britain to the Netherlands and eventually returned to Germany. He became a major figure in the German and international anarcho-syndicalist movement, helping to organize the International Congress in Berlin in 1922 leading to the formation of the International Workingmen's Association (IWA). Rocker was opposed to anarchist support for the Bolshevik Revolution after 1917 and led the libertarian socialist opposition to the growing Nazi movement in Germany.
In 1933 Rocker left Germany again to escape persecution by the new Nazi regime. Settling in the United States, he continued to work as a speaker and writer, directing his efforts against the twin evils of Fascism and Communism. He spent the last 20 years of his life as a leading figure in the Mohegan community at Crompond, New York, and was the best-known anarchist in the country until his death. He supported the Allies in the Second World War, which caused a breach with some old comrades, but he continued to receive more admiration and affection than any veteran of the movement since Kropotkin or Malatesta.
Rocker was a very prolific speaker and writer in both Yiddish and German, and he produced a great many articles and pamphlets and several books. Many of his writings were translated into Spanish and widely circulated in Latin America, but not many appeared in English. Apart from a few pamphlets, three books were published in the United States - Nationalism and Culture (1937), an essay in literary criticism called The Six (1938), and a popular survey of Pioneers of American Freedom (1949). Two more were published in Britain, Anarcho-Syndicalism (1938), and the section of his autobiography covering The London Years (1956). Some others were translated into English but not published like Behind Barbed Wire and Bars, an account of his internment during the First World War.