A constitution is the foundation of any democracy, and its text shapes the path of democratic development. But who chooses the framers of such a document? And how does this choice affect the composition and ultimate development of a constitution? To resolve this issue of political selection, Denmark adopted a lottery-based procedure to choose the members of its Constitution Committee in the creation of the “June Constitution” in 1848. Using a micro-level dataset of deputy biographies and constituent assembly archives, we analyze how this procedure affected the constitution drafting process. We show that the lottery-based procedure selected educated and experienced committee members, at the expense of noble and king-appointed deputies. We also show that this selection rule prevented the cooptation of the document by the radical left. Thus lottery-based selection played a sanitizing role during a period of democratization without developed parties, in the drafting of the constitution that governs Denmark to this day.