Son of a poor legal clerk, Bradlaugh served in the British army (1850–53), followed his father's occupation for a time, and then became an antireligious lecturer under the name of Iconoclast. In 1860 he took over the editorship of the periodical National Reformer, which was prosecuted (1868–69) for alleged blasphemy and sedition. From 1874 to about 1885 he was closely associated with Annie Besant (Besant, Annie), an advocate of numerous radical causes. In 1876 the Bristol publisher of Fruits of Philosophy, a birth-control pamphlet by Charles Knowlton, a physician in the United States, was given a light sentence for selling an indecent work. To vindicate their ideas of freedom, Bradlaugh and Besant republished the book in London in 1877 and circulated it aggressively, incurring much more severe penalties. Their indictments were nullified on a technical point, however.

In 1880 Bradlaugh, campaigning as a radical, was elected to the House of Commons. For more than five years, however, he was denied his seat because he asked to be allowed to affirm rather than to take the religious oath of Parliament. During that period he was reelected three times and later offered to take the oath but was forbidden to do so until finally, in January 1886, permission was granted and he was seated. By that time public opinion had swung in his favour, and Bradlaugh himself, who opposed Socialism, appeared increasingly conservative.