When the Bundestag created a committee to examine whether then-Chancellor Gerhard Schröder and others in the governing SPD party inflated economic figures before the 2002 federal elections to hide a growing budget deficit, he was chosen by his parliamentary group to lead the inquiry.

[19] Together with his French counterpart Delphine Batho, he put in motion the establishment of the French-German Office for Renewable Energies (L'Office Franco-allemand pour les énergies renouvelables) in 2013.

[22][23] In the negotiations to form a government following the 2013 federal elections, Altmaier led the CDU/CSU delegation in the energy working group; his co-chair from the SPD was Hannelore Kraft, Minister-President of North Rhine-Westphalia.

[25] In July 2015, Altmaier invited the United States Ambassador to Germany, John B. Emerson, to explain documents publicized by WikiLeaks that showed what appeared to be summaries of recorded conversations involving Chancellor Merkel or senior officials.

Shortly after, WikiLeaks released additional documents including Altmaier's telephone number, adding to a growing pile of allegations that United States intelligence agencies conducted extensive surveillance of the German government.

[27] From early 2017, he was a member of the German government's cabinet committee on Brexit at which ministers discussed organizational and structural issues related to the United Kingdom's departure from the European Union.

He was integral to the Pizza Connection, a group of moderate CDU and Green Party politicians – including Hermann Gröhe, Armin Laschet and Cem Özdemir – who met at Sassella, an Italian restaurant in Bonn.

According to Altmaier, the banks must be supported, in Greece and elsewhere, and the European Financial Stability Facility might have to issue guarantees for the holders of Italian and Spanish bonds, because they also fear that they will be asked to pay up.

[35] In his position as Minister for Economic Affairs, Altmaier has become a figurehead for efforts to strengthen the European Union's defences against the encroachment of US and Asian technology and healthcare companies.

[36] Also in 2019, he presented plans to set up a standing government committee which, as a last resort, could decide to temporarily take stakes in German companies that produce sensitive or security relevant technologies.

[37] In 2020, he introduced legislation giving the government a right to veto hostile foreign takeover bids for healthcare companies, a measure designed to ensure a continuous supply of essential products during the COVID-19 pandemic in Germany.