[4][2][3] Valstar started his career in 2009 as a communications advisor for the VVD, where he worked on its social media strategy, and he became a press officer of its parliamentary group in the House of Representatives in 2011.

[10] From that position, he proposed to name more streets in the municipality after local soldiers and resistance fighters in World War II.

[4] He became his party's spokesperson for fishery, nature, horticulture (a major industry in Westland), the countryside, animal welfare, war victims, and resistance fighters.

[14] Valstar co-filed motions to arm MQ-9 Reaper unmanned aerial vehicles, to allow tastings of cultured meat, and to call on the government to aid the greenhouse horticulture sector in cooperation with banks in a time of high natural gas prices.

[15][16][17] In September 2022 – during the Russian invasion of Ukraine – he joined Chris Stoffer (SGP) in the drafting of a bill to make sure defense spending would be at least 2% of Dutch GDP in accordance to a NATO norm.