Guillaume also worked as Manuel Valls's campaign director in the Socialist Party's primaries for the 2017 presidential election.

[5] 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.

[6] 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.

[8] Didier Guillaume was announced as the forthcoming Minister of State of Monaco on 10 June 2024, to succeed the incumbent Pierre Dartout for a four-year term beginning on 2 September.

[13][14] He was given a state funeral at Monaco Cathedral on 23 January that was attended by both Prince Albert II and French President Emmanuel Macron.