Thiériot previously served as Mayor of Beauvoir (2008–2018) and President of the Departmental Council of Seine-et-Marne (2018), in which he has represented the canton of Nangis since 2015.

[6][7] Ahead of The Republicans' 2022 convention, Thiériot endorsed Bruno Retailleau for the party leadership,[8] which was eventually won by Éric Ciotti.

In late 2023, Thiériot led a call to the government by seventeen The Republicans members of the National Assembly to help pass an immigration bill as amended by the Senate.

The members expressed their concern that a watered-down version of the bill would fail to pass the National Assembly;[9] it was indeed rejected prior to examination on 11 December 2023, a first of this political importance since 1998, according to Le Figaro.

[10] The bill finally passed by both houses of Parliament on 19 December 2023 was "hardened" compared to the failed version, as Thiériot had suggested.