Matthias Miersch (born 19 December 1968) is a German criminal defense lawyer and politician of the Social Democratic Party (SPD) who has been serving as Member of the Bundestag since the 2005 German federal election, representing the Hannover-Land II district.

[1] On 8 October 2024 Miersch was appointed as provisional secretary general of the Social Democratic Party.

Since 2013, Miersch has been a member of the party's executive board under successive chairpersons Sigmar Gabriel (2013-2017), Martin Schulz (2017-2018), Andrea Nahles (2018-2019), Norbert Walter-Borjans (2019–2021), Saskia Esken (since 2019) and Lars Klingbeil (since 2021).

In the negotiations to form a Grand Coalition of the Christian Democrats (CDU together with the Bavarian CSU) and the SPD following the 2013 federal elections, Miersch was part of the SPD delegation in the working group on the environment and agriculture, led by Katherina Reiche and Ute Vogt.

From 2014 to 2016, Miersch was one of the members of the country's temporary National Commission on the Disposal of Radioactive Waste, chaired by Ursula Heinen-Esser and Michael Müller.