Used to be the DDE with controlling power over planning/developing/environment.
I discovered by accident, The Mairie doesn’t necessarily have the last word. Planning and all things connected…
From “French property”
" The offices dealing with it in the préfecture used to be called the Direction Départementale de l’Equipement (DDE) , but the nomeculature is being changed to Direction Régionale de l’Environnement, de l’Aménagement et du Logement (DREAL).
The DREAL/DDE is the county planning and highways department and it has a network of local offices throughout each department.
Accordingly, unlike in the UK, it is potentially civil servants who decide your planning application and not the local politicians.
The mayor will formally sign the consent (or refusal) on behalf of the public authorities, but they will not always make the decision.
It is not entirely unusual for the préfecture to make a decision with which the mayor is at odds. If the mayor/local council disagrees with the opinion of the préfecture , and the council are not the planning authority, then they themselves can make an appeal to the préfet within two months of the decision.
Accordingly, do not always assume that all you need to do is get the mayor to support your application and that consent will be forthcoming.
The mayor will always be influential (and sometimes very influential with officials), but their point of view will not always be the determining voice.
At a minimum, you need to find out whether the local mairie has planning responsibility and, if they do not, the existence of any local plan.
Conversely, if the local council is the planning authority, then you could find the mayor making a decision that conflicts with the advise given to them by the DDE. They mayor is not obliged to accept the advice of the DDE (except in very particular circumstances). In which case, if you are unhappy with the decision you need to make an appeal to the prefecture, provided you feel there are planning grounds on which to do so.
In some cases small local councils have come together in an inter-commununal body ( Etablissement Public de Coopération Intercommunale (EPCI) ), to whom they have transferred responsibility for planning and certain other matters. In these cases, it is the Chairman of the inter-communal body who will have primary responsibility for planning decisions".