As a member of Alliance 90/The Greens, Hofreiter has been a member of the Bundestag since the 2005 elections. Between 2005 and 2013, he served as member of the Committee on Transport, Building and Urban Development; he served as chairman of the committee from 2011 until 2013. He was also member of the German-Austrian Parliamentary Friendship Group.
Hofreiter served as co-chair of the Green Party's parliamentary group, together with Katrin Göring-Eckardt from October 2013 to December 2021. In 2013, he was elected unopposed as the sole candidate of the group's left faction. In September 2019, both Hofreiter and Göring-Eckardt were unsuccessfully challenged by Cem Özdemir and Kirsten Kappert-Gonther.
In 2011, Hofreiter joined Gerhard Schick, Hans-Christian Ströbele and Winfried Hermann in their successful 2011 constitutional complaint against the refusal of Chancellor Angela Merkel's government to provide information on the Deutsche Bahn and financial market supervision. In its judgment pronounced in 2017, the Federal Constitutional Court held that the government had indeed failed to fulfil its duty to give answers in response to parliamentary queries and to sufficiently substantiate the reasons.
Since the 2021 elections, Hofreiter has been serving as chairman of the Committee on European Affairs. In addition to his committee assignments, he has been a member of the German delegation to the Franco-German Parliamentary Assembly since 2022.
Invitation-only event featuring Anton Hofreiter, who will discuss the IRA and the European response, the Net Zero Industrial Act.