Rix first became a member of the Bundestag in the 2005 German federal election.[2] He has since been a member of the Committee on Family, Senior Citizens, Women and Youth.[3] Since 2014, he has been serving as his parliamentary group’s family, senior citizens, women and youth.
Within the SPD parliamentary group, Rix belongs to the Parliamentary Left, a left-wing movement.[4]
Since 2019, Rix has been serving as deputy chairman of the SPD in Schleswig-Holstein. Ahead of the 2021 elections, he was elected to lead the SPD's campaign in Schleswig-Holstein.[5]
In March 2024, Rix announced that he would not stand in the 2025 federal elections but instead resign from active politics by the end of the parliamentary term.[8]