In 1977, he entered the Ministry of Interior as a technical counsellor of Christian Bonnet, an office which he held until François Mitterrand's election in 1981.

During the second cohabitation (Édouard Balladur's government), he was named deputy-director of Charles Pasqua's cabinet, who was at the time the Minister of Interior.

[7] Guéant has been the target of two investigative judge cases, including one where Sarkozy's 2007 campaign allegedly received donations from the government of Libya, under the reign of Col. Muammar el-Qaddafi.

[8] In October 2021, the Judicial Tribunal of Nanterre announced that Claude Guéant will be tried for "illicit financing" of his legislative campaign of 2012, because of the distribution of a leaflet in his favor by the mayor LR of Boulogne-Billancourt (Hauts-de -Seine).

On 21 January 2022, Guéant and three co-defendants, writer and one-time Sarkozy advisor Patrick Buisson, former cabinet director Emmanuelle Mignon and former pollster and consultant Pierre Giacometti, were found guilty of polling fraud involving allegations that they misused public money while ordering public opinion polls worth a combined 7.5 million euros ($8.7 million) during the course of Sarkozy's presidency between 2007 and 2012 and was sentenced to eight months in jail.