In 1973, he entered the government of Pierre Messmer as Secretary of State for Coopération, and was then named Secretary of State to the Ministry of Agriculture and Rural Development in the government formed by Jacques Chirac after the election of Valéry Giscard d'Estaing to the presidency of the French Republic in 1974. In 1976, J.F. Deniau became France's ambassador to Madrid, on the request of the new king Juan Carlos, with whom he had begun a friendship during regattas. Deniau would play an active advisory role to the king and the government during Spain's democratic transition following the death of general Franco.