This doctoral dissertation examines whether incumbency affects democracy, and if it does, how re-election impacts on the political system. This thesis links and extends two theoretical traditions that hardly ever have been combined: political support theory and incumbency theory. Political support theory is used as a proxy to examine democracy from a multidimensional perspective. In this theoretical tradition, there has been a considerable concentration of studies on developed nations, and which take a comparative approach. Also, there is persistently inadequate attention given to measuring the form of a government, with a strong predominance of parliamentarian systems. Likewise, most of the research is focused at the individual level, in where the use of statistical techniques is prevailing, and the mixed methods are, nearly, non-existent. On the other hand, there are no studies that explain incumbency effects on democracy directly. Despite there being plenty of inferences which can be taken from incumbency analysis and its extrapolations about democracy and elections, there is a scarcity of studies that associate both political phenomena. In most cases, scholars analyse incumbency as an advantage in popular elections in developed countries, mainly the U.S. The main argument of this thesis proposes that incumbency has effects on democracy and that those impacts will have adverse consequences on the democratic system. Taking Chile as a case-study, a developing country with a presidential system and with similarities to Western party systems, this research seeks to respond three hypotheses. 1) The categories of support identified by Booth and Seligson in 2009 could, to an extent, be modified by including questions that gauge the role of the presidential institution in the Chilean political system. 2) It is expected that incumbency will be shown to have distinct impacts on democratic political legitimacy. 3) The effect of deputies' re-election on political legitimacy dimensions will depend on the composition of legislative pairs at the electoral district level in Chile: two newcomers, one newcomer and one incumbent, or two incumbents. This investigation uses a mixed method strategy. From a qualitative perspective, I characterise all law bills proposed to the NC to limit the re-elections of public authorities in Chile, between 11th March 1990 and 31st December 2016. In line with this doctoral dissertationâs aims, a context analysis is used to analyse the content of draft laws related to incumbency. From a quantitative approach, I examine the legislative incumbency effects on political legitimacy dimensions in Chile, from 2008 to 2014. In line with this doctoral dissertationâs aim, a series of statistical techniques are used to analyse the effects of incumbency on political support. The findings suggest that: 1) The effects of incumbency are distributed differently according to the component of political legitimacy. 2) The rotation of political elites (seniority and the circulation of elected deputies) is the most substantial incumbency dimension to explain political support in comparison with the competition dimension. 3) The three indicators based on the margin of victory are only related negatively to support for government management. 4) The HDI has effects on political support, but they were inconsistent. 5) The legislative pair composition produces a moderator effect on incumbency indicators. 6) Politics and ideology play a pivotal role in understanding and explaining political support theory. This research concludes that is necessary to keep expanding studies that relate incumbency and democracy by taking other countries with different electoral systems, that arguments hold by politicians should be adjusted considering evidence, and it is imperative to reduce the perception-facts gap in citizens.