The institutional transition from the Second Empire to the Third Republic after 1870 allowed new figures to enter politics. Émile-Justin Menier, a rich chocolate manufacturer who built his fortune under the Second Empire, joined the republican camp in 1871. This article analyzes how this manufacturer soon succeeded in converting his financial resources into political and electoral resources. Combining strong local support with direct access to national republican networks, he became a distinctive figure of the republican camp. His originality lay in his overlapping involvements in business, science and politics. The disputes triggered off by his political career and by his struggle in favor of the implementation of a single tax on capital highlight the difficulties of the process of legitimizing the political competence of manufacturers and merchants. This resistance also sheds light on how professional politicians try to marginalize newcomers in politics. Lastly, Menier’s social and political career illustrates the changing forms of republican politics and announced the birth of a new category in the public sphere, namely the representation of the “taxpayer’s interests”.