As one of the state's representatives at the Bundesrat, Steffen was a member of the Committee on Legal Affairs from 2015 until 2020.

[6] That same year, he joined the Commission for the Reform of the Electoral Law and the Modernization of Parliamentary Work, co-chaired by Johannes Fechner and Nina Warken.

[7] In addition to his committee assignments, Steffen has been a member of the German delegation to the Franco-German Parliamentary Assembly since 2022.

[8] Amid the COVID-19 pandemic in Germany, Steffen joined forces with six other parliamentarians – Dirk Wiese, Heike Baehrens, Dagmar Schmidt, Janosch Dahmen, Katrin Helling-Plahr and Marie-Agnes Strack-Zimmermann – on a cross-party initiative in 2022 to support legislation that would have required all adults to be vaccinated.

[10][11] Together with Marco Wanderwitz, Carmen Wegge and Martina Renner, Steffen was one of the initiators of a 2024 cross-party initiative to request that the Federal Constitutional Court issue a ban of the far-right Alternative for Germany party.