Marcin Kierwiński was born on 22 August 1976 in Warsaw. He obtained two master’s degrees in engineering from Warsaw University of Technology (at the Faculty of Electronics and Information Technology and the Faculty of Production Engineering). He also completed postgraduate studies at the ORGMASZ Institute of Organisation and Management in Industry.

His career as a public servant started at the local government level, after he was elected as a City Councillor of the Capital City of Warsaw. In 2010, he was appointed Deputy Marshal of the Mazovian Voivodeship, followed up with a seat of the alderman of the Mazovian regional assembly in the 2010 election, as well as his second term of office as a Deputy Marshal.

In 2011, he secured a seat of the member of the Polish Sejm in 2011, following a campaign in Warsaw. In the subsequent parliamentary elections in 2015, 2019 and 2023, he ran as a candidate in the Płock district and continued to garner trust, securing his seat four consecutive times. In the 2023 election, his result surpassed all the candidates in the district.

In 2015, he served as Secretary of State in the Chancellery of the Prime Minister, as well as the head of the Political Cabinet of Prime Minister Ewa Kopacz. He has been secretary general of Platforma Obywatelska (Civic Platform) since 2020.

From 2000 to 2007 he was an employee of PZL Warszawa-Okęcie, in 2007 he was appointed Vice-President of the Board at IF Max-Film, and in 2007-2010 he worked as Vice-President of the Board of Warsaw-Modlin Airport.