One key component of modern constitutions is the representative system. The often-contested codification of this system over time in democratizing political orders depends on a number of factors, such as the existing institutional setting, the power relations of important political actors, and the ideational resources, or political culture, available to the constitution drafters. This article examines the ideational resources drawn on by the members of Thailand’s 2007 Constitution Drafting Committee (CDC) in debating and deciding the shape of the National Assembly’s upper house, the Senate. This is mainly done by analysing the word-by-word minutes of their meetings. The respective processes of the 1997 CDC are described more briefly in order to provide background on an area of constitutional contestation that found its latest expression in November 2013, when the Constitutional Court invalidated the National Assembly’s constitutional amendment, which would have reintroduced a fully elected Senate. The article contextualizes these developments by reference to mass protests against the “Thaksin regime” that had been organized since November 2013 by the so-called People’s Democratic Reform Council (PDRC).