From 1978–1984, he was deputy leader of a part (Westfalen-Lippe) of the North Rhine-Westphalian branch of the Junge Union, the CDU youth organization.

In his capacity as president, he chairs the parliament’s Council of Elders, which – among other duties – determines daily legislative agenda items and assigning committee chairpersons based on party representation.

Lammert's tenure in office gained him recognition across party lines as he was determined to uphold the honor and importance of the federal parliament while at the same time displaying a dry, sophisticated sense of humor most notably in exchanges with then-chairmen of Die Linke Gregor Gysi.

In the negotiations to form a Grand Coalition of the Christian Democrats (CDU together with the Bavarian CSU) and the SPD following the 2013 federal elections, Lammert was part of the CDU/CSU delegation in the working group on cultural and media affairs, led by Michael Kretschmer and Klaus Wowereit.

When Federal President Joachim Gauck announced in June 2016 that he would not stand for reelection, Lammert was soon mentioned by German and international media as likely successor.

[3][4] In October 2016, Lammert announced that he would not stand in the 2017 federal elections and resign from active politics by the end of the parliamentary term.

Since 2022, following an appointment by Chancellor Olaf Scholz, Lammert has been serving on a three-member panel (alongside Krista Sager and Andreas Voßkuhle) to assess potential conflicts of interest, requiring senior German officials from the chancellor to deputy ministers to observe a cooling-off period if they want to quit the government for a job in business.

[13] Ahead of Egyptian president Abdel Fattah el-Sisi's first official visit to Germany in June 2015, Lammert announced that he would not meet the former army chief, citing "an unbelievable number of death sentences".