Based on research in nearly thirty archival centers including newly-discovered family archives, as well as field studies in France, Russia and Vietnam, this dissertation sets out to fill an important gap of the history of the French Republic: despite 25.000 roads in France named after Paul Doumer (1857-1932), the thirteenth President of the French Third Republic (1931-1932), no study has yet been dedicated to him. General-Governor of Indochina (1897-1902); the only genuine worker's son among the leading elites of the Third Republic; the only teacher among the fourteen Presidents of the Third Republic; one of the few who successively presided over each of the two Chambers but, on the other hand, who did not chair the government or any political party: Paul Doumer's career represents many exceptions. Doumer took an active role on every important political issue from 1887 to 1932, particularly colonial expansion, the three-year law, the income tax and the reparations to Germany. Embodying the meritocratic dimension of the French republican model and the ideal of social promotion based on schooling and individual talent, Paul Doumer's cursus honorum to the supreme office is also marked and shaped by tragedy: the Great War cost the lives of four of his five sons before the President himself was shot on 6 May 1932 while exercising his duties. The drama was dubbed the "Sarajevo of the Second World War", coming at a time when fascism was on the rise in Europe.