Early beginnings

In 2004, after his election as President of the General Council of Drôme, Guillaume resigned his post as Mayor of Bourg-de-Péage, which he had held since the 1995 municipal election. The town is the chef-lieu of the canton of Bourg-de-Péage, represented by Guillaume in the Drôme General Council from 1998 until 2015.

Senator for Drôme, 2008–2018

In 2008, Guillaume was elected to the Senate. He served as First Vice President of the Senate under the leadership of President Jean-Pierre Bel from 2011 to 2014, when he became president of the Socialist group and Leader of the Opposition in the Senate, as the right had won a majority at the 2014 election.

After leaving the presidency of the Drôme General Council following the victory of The Republicans at the 2015 departmental election, he was succeeded by Patrick Kanner as group president in the Senate in 2018. Guillaume also worked as Manuel Valls's campaign director in the Socialist Party's primaries for the 2017 presidential election.^[2]

Minister of Agriculture, 2018–2020

Guillaume served as Minister of Agriculture and Food under Prime Minister Édouard Philippe from 2018 to 2020, succeeding Stéphane Travert. After taking office, he vowed to take his decisions "in independence" from the industry lobbies.^[3]

Guillaume stated he would run for Mayor of Biarritz in 2020 against fellow government member Jean-Baptiste Lemoyne, but they both withdrew their candidacies before the election.

During the COVID-19 pandemic, Gulliaume called on unemployed citizens to help the country's farmers in their production process as seasonal foreign workers were absent. 50,000 people responded favourably.^[4] He was succeeded by Julien Denormandie and retired from politics.