Mario Czaja (born 21 September 1975) is a German politician of the Christian Democratic Union (CDU) who has been serving as a member of the German Bundestag since the 2021 elections.

Czaja served as the party's Secretary General from 2022 to 2023, under the leadership of Friedrich Merz. From 2006 until 2021, he was a member of the State Parliament of Berlin.

Czaja was born 1975 in East Berlin, the capital of East Germany, and studied business administration. From 1997 until 2000, he worked at insurance company Nürnberger Versicherung.

Czaja entered the CDU in 1993 and became member of the State Parliament of Berlin in the 1999 state elections. He served as his parliamentary group's spokesperson on health policy from 2001 until 2011.

From 2011 to 2016 Czaja was also member of the Senate of Berlin, the government body of Berlin, with responsibility for health care and social issues. At the time, he was the youngest member of the state government led by Governing Mayor Michael Müller.

In 2012, Czaja – together fellow state ministers Frank Henkel and Thomas Heilmann – unsuccessfully advocated for a reduction in the penalty-free personal use of cannabis from 15 to six grams. Also during his time in office, he appointed former state government members Eberhard Diepgen, Heidi Knake-Werner, Ingrid Stahmer and Wolfgang Wieland as advisors on the city's migration policies in 2014. In 2016, Czaja cancelled the government's contract with one of the city's largest operators of hostels for asylum seekers after newspapers B.Z. and Bild printed internal emails showing the company's managers joking about building a guillotine and crematorium for refugee children.

Czaja was a CDU delegate to the Federal Convention for the purpose of electing the President of Germany in 2017.

From 2018 until 2021, Czaja served as his parliamentary group's deputy chair, under the leadership of Burkard Dregger. During that time, he was also a member of the Committee on Education, Youth and Families.