The departure of French Foreign Minister Laurent Fabius from the country's socialist government had long been rumoured. The same rumour mills have suggested that Ségolène Royal, Elisabeth Guigou, Jean-Marc Ayrault or Matthias Fekl could possibly replace him.
The 69-year-old was France's youngest-ever prime minister when he took the role aged 37 in 1984.
Shortly after his resignation on Wednesday, French President François Hollande officially put forward Fabius's nomination as head of the country's Constitutional Court, in a presidential communiqué.
The former foreign minister was widely praised for his role overseeing the successful UN climate negotiations in Paris last December. As host of the global talks, Fabius presided over 13 days of gruelling talks to get 195 nations plus the European Union to agree on transforming the energy system underlying the world economy.
While fending off rumours of ill health -- and a persistent suggestion that he suffered from Parkinson's -- Fabius threw himself into the complex world of climate science and politics for two years preceding the talks. He made 12 trips to China, four each to India and Saudi Arabia, and also went to Brazil and South Africa to get them onboard and attempt to understand their concerns.
France retains the Cop21 presidency until the end of the calendar year when Morocco will take up the agenda for Cop22.
Speaking on a separate issue on Wednesday, Fabius told journalists he thought it was unlikely that US President Barack Obama would advance the Syrian peace process as much as his US counterpart, John Kerry has suggested.