On a local scale, Luc Guyau has first been elected chair of the Local Center of Young Farmers (1975–1978)and Chair of the Local Federation of Agricultural Unions FDSEA in Vendée (1984–1996).
On the national level he became President of the National Center of Young Farmer CNJA (1982–1984), prior to his election at the top of the National Federation of Agriculturals Unions FNSEA from 1992 to 2001 and his election at the Presidency of the COPA (Comité des organisations professionnelles agricoles de l’Union européenne) from 1997 to 1999.
He chaired the Chamber of Agriculture of Vendée Chambre d'agriculture and was deputy chairman of the regional chamber of Pays de la Loire from 1995 to 2010.
Luc Guyau chaired the Permanent Assembly of Agricultural Chambers from 2001 to 2010. He is a member of the CESE Conseil économique, social et environnemental (CESE) (France), of the COPA and the FIPA (Fédération internationale des producteurs agricoles). From 2001 to 2011 he was the vice-chair of the CESE Conseil économique, social et environnemental (CESE) (France).
He is deputy chairman of the board of AgroParisTech. He is also a member of the UMP.
In 2009, he has been appointed by the French Government to be candidate at the Presidency of the FAO. He was elected in the framework of the Conference on 24 November 2009 and succeed to Mohammed Saeid Noori-Naeini.
He then left his national and local duties and Guy Vasseur succeed him as the Chairperson of the Permanent Assembly of Agricultural Chambers.
On July 2, he was reelected as Independent Chairperson of the FAO Council at the 37th FAO Conference, for a second 2-year mandate.
Luc Guyau's deep humanism led him to co-found the Terrethique organization that aims to increase public awareness on agriculture, fooding, natural resources management issues taking the question "How will we eat tomorrow?" as its main entry point.
In June 2011, he took position on the issue of the reform of the European Programme of Food Aid to the most deprived raising public awareness on the urgent need to find an agreement at the European Council level in order to rescue European food aid organizations. On November 14, an agreement was reached in order to secure PEAD founding for 2012 and 2013. In late 2011 he contributed to place the issue of urban-rural linkages on the agenda, questioning the validity and sustainability of the current urbanization trends. In this framework he condemned the urbanization dynamics that lead to the "slumisation" of the urban peripheries and land conflicts across the world. He stands for the design and implementation of food-wide policies that take into account the diversity and complexity of linkages between urban and rural areas on a food and agriculture prospective and allow a balanced development of both spaces.
His views on agriculture, based on an equilibrium between people, products and territories have been detailed in two books:Earth, landscapes and our food/La Terre, les paysages et notre alimentation, Éditions du Cherche Midi, 1998
The agricultural challenge/'Le Défi paysan, Éditions du Cherche Midi, 2000
He also published:A Chamber of Agriculture, what for?/A quoi sert une Chambre d'agriculture?, Éditions de l'Archipel, 2000