Secret ballot systems aim to ensure voter anonymity and thereby thwart attempts at voter intimidation or vote buying. The secret ballot is thus a key institutional innovation in the process of democratization. Surprisingly, little empirical evidence exists on its effectiveness. In this paper, we take advantage of four direct-democratic votes between 1866 and 1877 in Switzerland, all concerning franchise extension to the same previously excluded groups. In each case, a majority of the voters rejected franchise extension. In line with the existing literature on concentrated resource endowments and democratization, we show that landholding inequality decreases support for suffrage extension. We argue that this negative relationship between landholding inequality and local support for suffrage extension reflects pre-industrial forms of social power and control, which undermine democratization preferences of the local population. The introduction of the secret ballot in 1872 allows us to examine whether anonymity enables voters to escape these processes of social control and express their political preferences more freely. We show that the introduction of the secret ballot significantly reduces the negative impact of landholding inequality on support for suffrage extension. Moreover, factors influencing the ability of local landlords to exercise social control – population density and distance to the political capital – moderate the relationship between the secret ballot, landholding inequality, and support for suffrage extension. Together, this evidence suggests that the secret ballot was effective in curtailing local elites’ ability to manipulate political processes.