This thesis is a study of the feminist dimension of Freethought in nineteenth-century Britain, and the part played by freethinking critiques of Christianity in the Victorian women's movement. `Infidel feminists' saw religion, specifically Christianity, as the root of women's oppression and equated female emancipation with liberation from the bonds of superstition. This distinctive brand of feminism was advocated by the Freethought movement as part of its wider agenda to rid society of false and repressive belief-systems through the critique of orthodox religion. Organised Freethought was home to a small number of prominent female activists who developed and promoted this `Freethinking feminism'. For these women the rejection of religion encouraged and shaped support for women's rights. Freethinkers' commitment to moral autonomy, free speech and the democratic dissemination of knowledge, their rejection of God-given notions of sexual difference and their critique of the Christian institution of marriage, provided powerful intellectual tools with which to challenge dominant and oppressive attitudes to womanhood. Infidel feminists criticised, engaged with and contributed to the wider women's movement. It is therefore argued that although nineteenth-century feminism was predominantly Christian, it was built around religious controversy and contestation rather than a unified adherence to a particular set of religious values. The argument presented has important implications for existing scholarship on both feminism and secularisation. It is the first in-depth study of Freethinking feminism, which has been almost entirely neglected in histories of First Wave feminism. A fuller understanding of the important role played by the `infidel feminists' enables us to identify a more continuous feminist tradition throughout the century, connecting the more `radical' Owenite feminists of the 1830s and 40s with the more `respectable' post-1850 women's movement. By showing how Freethinking feminism developed not only in opposition to, but also in dialogue with, Christian debates on women, the thesis contributes to current rethinking of the `religious'/`secular', distinction, demonstrating that these categories should be viewed as interdependent rather than merely oppositional. As the thesis shows, the Christian faith, against which infidel feminists campaigned so vigorously, fundamentally structured their Secularist commitments.