De Mos became a member of the House of Representatives in 2009, succeeding Barry Madlener, who had been elected into the European Parliament.

Although reelected in 2010, De Mos was not selected to contest in the 2012 general election by party leader Geert Wilders.

[2] In the 2021 general election, De Mos attempted to return to the House of Representatives as lijsttrekker of the party Code Orange.

[5] He subsequently became First Deputy Mayor of The Hague and alderman for economic affairs, sport and public space.

[6] On 1 October 2019, his offices were raided by the Dutch intelligence police as part of an investigation into alleged corruption.