After being active in the FDP and the Young Liberals in der Beek in the 1980s, his membership was then suspended for 20 years and he finally resigned from the party, he re-registered with the Free Democrats in 2013. In parliament, in der Beek served on the Committee on Economic Cooperation and Development (from 2018), the Committee on the Environment, Nature Conservation and Nuclear Safety (from 2018) and the Subcommittee on International Climate and Energy Policy (since 2022). Following the
2021 elections, he served as his parliamentary group’s spokesperson for climate action. In addition to his committee assignments, in der Beek was part of the German Parliamentary Friendship Group for Relations with the Southern African States and the German Parliamentary Friendship Group for Relations with Arabic-Speaking States in the Middle East. In the negotiations to form a so-called
traffic light coalition of the
Social Democratic Party (SPD), the
Green Party and the FDP following the
2021 German elections, in der Beek was part of his party's delegation in the working group on
environmental policy, co-chaired by
Rita Schwarzelühr-Sutter,
Steffi Lemke and
Stefan Birkner. In 2024, in der Beek announced that he wasn't seeking re-election for Bundestag. == Other activities ==