This dissertation examines transnational reform networks in the Atlantic World—specifically between the United States and Great Britain—between the War of 1812 and the passage of the Second Reform Act in Britain in 1867. This period saw the rise of a transnational humanitarian tradition built atop the successful campaign to end the British slave trade in the second half of the eighteenth century. A new transatlantic reform system, constructed around feedback loops of persons and print, was coming into being. In the six decades leading to the American Civil War, Britons and Americans constructed a multifaceted transatlantic network of reform communication that exerted a novel transnational pressure politics. A multitude of reform movements—including abolitionism, women’s rights, temperance, and Universal Peace—interwove in this Anglo-American reform pathway. This dialogue was rooted in and sustained by a spectrum of natural rights beliefs filtered through a prism of reformist Christian convictions. Four principles were paramount: the equality of all people, the inherent worth of the individual as a divinely-created being, the necessary freedom to develop and further oneself, and the unity of the human race. Espousals of these truths were the transatlantic fuel of this reformist revolution. Binding these various humanitarian beliefs together was a foundational commitment to the transcendent value of the human being, a value that had to be defended from the harmful tendencies of earthly governments and societies. This was the birth of a Natural Rights Atlantic, a geo-moral space defined by transnational appeals to human connection and individual liberation in which the ideas and activities of humanitarian reformers from different movements intermingled.