He served as parliamentary group leader of the ruling CDU/CSU faction in the German Bundestag from 2005 to 2018,[1] during which he was frequently referred to as the "right hand" of Chancellor Angela Merkel.

In early 2005, Merkel nominated Kauder as Secretary General of the CDU, after his predecessor Laurenz Meyer was forced to quit over payments he had received from his past employment with RWE, the power company.

[5] Ahead of the 2005 federal elections, he became Merkel's confidante and campaign coordinator while spearheading CDU proposals to increase VAT by 2 per cent to fund non-wage labour cost-cutting.

In the negotiations to form a coalition government following the 2013 federal elections, Kauder was part of the 15-member leadership circle chaired by Angela Merkel, Horst Seehofer and Sigmar Gabriel.

[21] He courted controversy the same year when he declared, in the context of ongoing European austerity measures, that, "Suddenly Europe is speaking German.

"[23] In discussions on whether there would be a renegotiation of France's 2015 deadline for bringing its deficit in line with the EU Stability and Growth Pact’s limit of 3 percent, Kauder said in a parliamentary debate that it was "high time that everyone understood that we must uphold the rules that we have adopted as law".

[24] In August 2014, Kauder called for the EU to adopt common arms export regulations, saying there would be an increasing number of European defense companies in the future, "especially German-French ones.

"[25] Reacting to revelations about NSA surveillance activities in Germany in 2013, Kauder blamed the United States for a "grave breach of trust" and demanded it should drop its "global power demeanor.

"[26] However, he did not want a publicly accessible investigation into the claims of US surveillance of chancellor Merkel's mobile phone, insisting that only a secretly operating committee can effectively handle the issue.