Mr Ayrault is likely to have a greater say in formulating policy than some of his predecessors, as the president has indicated that he will leave day-to-day business to the government.
His contacts at European level, in particular his expertise on Germany, have already come in useful to Mr Hollande.
As a special adviser during the election campaign, he had the task of liaising with other European left-wing parties. Now, Mr Hollande will look to him to help find common ground with Chancellor Angela Merkel over reviving growth in the eurozone.
Jean-Marc Ayrault – Profil av en ny statsminister #BBC