In this paper we measure the effect of social networks on politicians' career development. To this purpose, we construct a unique data set that contains information on the social network of the entire electorate of a sovereign nation, the 15th-century Republic of Venice. We identify the careers of 2.500 married politicians from the period between 1400 and 1524. Analyzing this panel of data we provide evidence that marrying the daughter of a more central father significantly improves the husband's career prospects in politics. Moreover, we show that this effect is independent from other characteristics of either families, like historical prestige, wealth or voting power (family size), and it is not biased by assortative marriages.