He served as parliamentary leader of the FDP in the Abgeordnetenhaus of Berlin from 2016 to 2023, and was lead candidate for the party in the 2016, 2021 and 2023 state elections.

[1] He graduated from Klingenberg high school in Biesdorf in 2000, and attended the Oberstufenzentrum Energietechnik II from 2000 to 2004, where he obtained a subject-specific university entrance qualification.

[2] His decision to change parties was motivated by a dispute over public subsidies to the Arche soup kitchen in Hellersdorf.

His defection saw the FDP group in the Marzahn-Hellersdorf council achieve official faction status, and Czaja became its chairman.

His actions caused considerable controversy, and he was voted the second most-unpopular person in Berlin in 2005, behind Hartmut Mehdorn, the CEO of Deutsche Bahn.

[2] He sought re-election to the Abgeordnetenhaus in the 2011 Berlin state election, running at the top of the FDP's in Marzahn-Hellersdorf party list.

After the municipal elections in Steglitz-Zehlendorf, where Czaja is district chairman, the FDP joined a traffic light coalition and displaced the CDU as governing party for the first time in fifty years.

[9] In November 2017, it was reported that Czaja and his FDP colleague Thomas Seerig had been receiving a publicly-funded €1,000 monthly allowance for an office that had not yet been constructed.

After months of debate, in June 2018, the Abgeordnetenhaus passed a resolution declaring that the referendum could not be implemented by the state government.

In addition, he is an ambassador for the Sport against Violence association, which aims to provide alternatives and perspectives for young people in difficult urban environments.

[2][5] After the successful FDP campaign in the 2016 Berlin state election, the party and executive agency HEIMAT received the 2016 Politikaward from the trade journal Politics & Communication in the Political Campaign, Digital Public Affairs, and Viral Communication categories.

"[16] In 2016, the business magazine Capital included Czaja in their "Rising Stars" list in the category "Politics and Communication".