This Essay argues that the constitutional framework of US colonial rule in the Philippines can be traced to that of British rule in the American colonies. Drawing from the concept of the “transatlantic constitution” developed by Mary Sarah Bilder, the existence of a “transpacific constitution” is shown, first, by comparing and contrasting British and American imperial legal agents and institutions, and arguing that the American institution of the Insular Government in the Philippines finds its origins in the US territories and ultimately in the British Empire’s colonial governments in America. Second, this Essay examines how the Supreme Court of the United States, in legitimating the American imperial constitution in the Insular Cases, mirrored the British imperial constitution. The dynamic of the “transpacific constitution” is illustrated in cases appealed from the Philippine Supreme Court to the US Supreme Court.