Gauweiler is considered a Euro-sceptic and made a name with partly successful constitutional complaints against the euro bailout fund and the Lisbon Treaty.

[5] Along with fellow lawmakers including Monika Grütters, Luc Jochimsen and Claudia Roth, Gauweiler traveled to Iran in 2010 to meet with Ali Larijani, Manouchehr Mottaki and others; the trip was heavily criticized by international human rights organizations.

[7] Following the 2009 federal elections, Gauweiler was part of the CDU/CSU team in the negotiations with the FDP on a coalition agreement; he joined the working group on foreign affairs, defense and development policy, led by Franz Josef Jung and Werner Hoyer.

In November 2013, Gauweiler was elected deputy chairman of the CSU,[8] in what was widely considered a move to appease the eurosceptic elements within his party.

[9] He resigned the post and his seat in the Bundestag on 31 March 2015, about three months before his 65th birthday; he had previously been strongly criticized by CSU leader Horst Seehofer for voting against the extension of financial aid for Greece.

[11] Over many years, Gauweiler has led several attempts to have the German constitutional court block measures that he considers enhance the EU’s powers at the cost of national sovereignty.

[12] Although his legal cases have generally failed, he has gained support from conservative voters, including members of the eurosceptic AfD party.

[20] Gauweiler claimed that the ECB's bond-buying program threatened Germany with unlimited losses,[21] arguing that it is an additional ground to reject use of German tax revenue for the rescue fund.

"[27][28][29] On September 12, 2014, Gauweiler traveled to Moscow to open the "Year of Language and Literature in Russia and Germany" as chairman of the Bundestag subcommittee on foreign cultural and educational policy.

[32] Among other high-profile cases, the firm represented Gauweiler’s friend[33] and onetime media mogul Leo Kirch in a multibillion-dollar lawsuit against Deutsche Bank.

[34] Notable clients also included the Government of Qatar,[35] Wirecard[36] and M. M. Warburg & Co.[37] In 2021, Süddeutsche Zeitung revealed that Gauweiler had been receiving consultancy fees amounting to more than eleven million euros by eurosceptic billionaire August von Finck during his time in parliament.