[1] He became a member of Forum for Democracy (FvD) in May 2018, nearly two years after its founding, and he was elected to the Provincial Council of North Holland in March 2019.

[1][4] Dekker ran for the House of Representatives in March 2021 as FvD's ninth candidate, and he was not elected as the party won eight seats.

[5] Between 23 August 2022 and 27 March 2023, he replaced Simone Kerseboom as a member of parliament during her maternity leave.

[1][3] He lost his bid for re-election to the Provincial Council of North Holland, but he remained a member due to Thierry Baudet declining his seat.

[3][6][8] Dekker was again sworn into the House of Representatives on 19 November 2024, replacing Pepijn van Houwelingen, who stepped down to take care of his pregnant wife.