Schneider joined the
SPD in 1995. He became active in
Young Socialists in the SPD and eventually was elected chairman of the Thuringian chapter. Until 2017, he also belonged to the leadership of the SPD in Thuringia. In the
1998 federal elections, at age 22, Schneider became the then-youngest representative in the German Parliament, representing
Erfurt from 1998 to
2005 and the successor constituency of
Erfurt – Weimar – Weimarer Land II since 2005. He was a member of the Budget Committee, where he served as his parliamentary group's
rapporteur on the budgets of the
Federal Ministry of Education and Research and the
Office of the Federal President. He is also a member of the Thuringian SPD parliamentary caucus, of which he became speaker in 2005. From 2008 to 2010, Schneider was a member of the parliamentary body providing oversight of the
Special Financial Market Stabilization Funds (SoFFin). In 2012, Schneider was selected as one of three speakers of the
Seeheim Circle. In the negotiations to form a
Grand Coalition of the Christian Democrats (
CDU together with the Bavarian
CSU) and the
Social Democrats (SPD) following the
2013 federal elections, Schneider was part of the SPD delegation in the working group on financial policies and the national budget, led by
Wolfgang Schäuble and
Olaf Scholz. He had previously publicly expressed his doubts about the Social Democrats joining a coalition government with the CDU/CSU, having preferred a coalition with the center-left
Alliance '90/The Greens. (2025) Following the formation of the
third cabinet of
Federal Chancellor Angela Merkel, Schneider served as deputy chairman of the SPD parliamentary group under the leadership of
Thomas Oppermann. He was also the chairman of the so-called
Confidential Committee (
Vertrauensgremium) of the Budget Committee, which provides budgetary supervision for Germany's three intelligence services,
BND,
BfV and
MAD. In addition, Schneider has been a delegate to the Conference established under Article 13 of the
European Fiscal Compact since 2014; this body assembles members of the relevant committees of the
European Parliament and national parliaments to discuss economic and fiscal policy and other matters concerning stability, coordination and governance in the
Economic and Monetary Union of the European Union. Following the
2017 election, Schneider succeeded Christine Lambrecht as
First Secretary of the SPD parliamentary group, in this position assisting the group's chairwoman
Andrea Nahles. In this capacity, he was also a member of the parliament's
Council of Elders, which – among other duties – determines daily legislative agenda items and assigns committee chairpersons based on party representation. Ahead of the
2021 elections, Schneider was elected to lead the SPD campaign in Thuringia for the fourth consecutive time. In the negotiations to form a so-called
traffic light coalition of the SPD, the
Green Party and the FDP following the elections, he led his party's delegation in the working group on economic policy; his co-chairs from the other parties were
Cem Özdemir and
Michael Theurer. ==Other activities==