This paper aims to bring to light the radical and subversive ideas of the British Enlightenment philosopher Mary Astell. It will be argued that Astell, despite her strict Anglicanism and affiliation with the rather conservative Tories, articulates radical thoughts on questions of gender equality. As will be shown, she is highly critical of contemporary sexual hierarchies, which is evident from her fierce criticisms of customary, natural, and scriptural defenses of patriarchalism. Part of her review of such hierarchies entails her ruthless assessment of the contemporary condition of marriage and the subordination of women therein. Besides reviewing and systematizing her critical positions, it is a further aim of this paper to compare these with her otherwise conservative ideas, such as denying a right to resistance or disobedience; a tension other commentators have tried to solve as well. I argue that, what we find in Astell, is a thinker who holds views many radicals would have concurred with, concerning both the spiritual and political equality of women.