A transformation of labor relations in antebellum America pushed the Jeffersonian republican frame to its breaking point, drawing reformers into the wider ambit of transatlantic social-democratic politics. Nineteenth-century social-democratic thinkers invoked the emancipatory ideas of Thomas Paine and “Gracchus” Babeuf, the critique of political economy by Owenite socialists, and the conception of a divided peuple by the French revolutionary Constantin-François Volney, to forge a new kind of politics in response to what contemporaries called the “social question.” American labor reformers reached across national barriers to grasp the common predicament facing wage workers. And, like their European counterparts, they saw a civil society divided against itself, where a republican polity could not stand. The article focuses on the articulation of novel social themes in the political consciousness of labor reformers, which became an integral part of the transatlantic debates over a global “social republic,” a proposal to extend the reach of political power into the international sphere of social production and exchange. It shows how the development from radical republican ideas to social-democratic reform did not follow a unilinear path, moving neatly from old to new concepts. Core concerns remained constant: independence, the common good, and the rights of laboring citizens. Yet while the new ways of thinking about society were born in the shell of the old republican language, its content and application transformed. As pressure on domestic production in antebellum America gave rise to a dependent wage worker, debates across workingmen’s clubs, newspapers, and pamphlets displayed a growing anxiety over a novel “social tyranny” and the “tendencies of modern society to sink the masses in poverty and ignorance.” These unprecedented changes put into question the long-standing belief that American workers would be spared the unhappy fate of their European counterparts. In the age of capital, a shared condition tied social reformers on both sides of the Atlantic. In the United States, reformers diagnosed the problem as the “non-recognition and non-guarantee” of one of the “great fundamental rights of man … the right of labor,” which rendered all “other rights … to a very great extent unavailable and worthless.” To wrangle the otherwise unbridled transformation of society, nineteenth-century social democrats demanded greater control over the conditions of production which, they argued, held the republic hostage. The article traces the movement of ideas across antebellum labor reform circles calling for shorter hours, including the early Workingmen’s Parties of Boston and Philadelphia; Lowell’s women labor organizations; and the New England campaign for a “Second Independence Day.” It also takes up the common concerns as well as emerging differences among these reformers, which distinguished social-democratic horizons from republican ideas. Through newspapers, pamphlets, speeches, and organizational minutes, this article connects laborers’ demands and intellectual genealogies across the Atlantic world, focusing on efforts in New York, Philadelphia, New England, Paris, and London as the centers of metropolitan life in the nineteenth century.