This paper attempts to identify the sources of Anna L. Barbauld’s pessimistic vision of the future Britain, which distinguishes her from her fellow Dissenters, especially Joseph Priestley. A millennialist outlook on history pervades Priestley’s An Essay on the First Principles of Government (1768), a defense of the rights of Dissenters, and his 1788 sermon on the slave trade. Here Priestley’s commitment to radical causes is based on the assumption that the course of human history is progressive―that even social evils of slavery and religious discrimination are part of the process by which the human race is progressing towards a free, just society under God’s providence. Barbauld, however, departs from an optimistic view of history held by her co-religionists. Her engagement with issues of Dissent, An Address to the Opposers of the Repeal of the Corporation and Test Acts (1790), is full of unwomanly rage at an infringement of Dissenters’ civil rights, which seemed to her a betrayal of the ideals of liberty that the British had upheld. Her Epistle to William Wilberforce (1791) also unleashes fury at the appalling state of moral decay in her country. In the poet’s judgment, Britain is doomed to self-destruction by not abandoning slavery and hence extinguishing the spirit of liberty. Barbauld’s break with the mainstream of Dissenting thought, i.e., her apocalyptic vision of the nation’s decline and fall, becomes more evident in Eighteen Hundred and Eleven (1812). As a liberal Dissenter, Barbauld had a firm belief in the idea of individual liberty and so found herself despairing of the political state of Britain, which gradually distanced her from Dissenting millenarianism. This distance made her political writing truly radical.