[2] Afterward, he was enlisted in the Reich Labor Service and experienced the end of World War II within its ranks.

However, in February 1953, he was delegated to his first three-year course at the Karl Marx Party Academy, which he completed in August 1955, earning a diploma in social sciences.

[1][2] Due to the double responsibilities of distance learning and party activities, he was relieved of his role as secretary in the district leadership in 1963.

In February 1974, when the Second Secretary of the Bezirk Neubrandenburg SED, Gerhard Zettler, was replaced, Müller was appointed as his successor at the district delegates' conference held in mid-February 1974.

[2][3] This made him the second most powerful figure in the Bezirk after the First Secretary Johannes Chemnitzer, and effectively chief of staff of the local SED leadership.

In April 1980, following intense internal criticism reported anonymously to Erich Mückenberger, the then-chairman of the Central Party Control Commission, Alois Bräutigam, the long-standing First Secretary of the SED in Bezirk Erfurt, resigned from his position, officially citing health reasons.

[6] He was also viewed as a hardliner: During the summer of 1989, he delivered several speeches praising the violent suppression of the student unrest in China as exemplary.

On the same day, the newly elected Central Party Control Commission of the SED, chaired by Werner Eberlein, convened for the first time.

They laid out provisions to hold both former First Secretaries, Hans Albrecht of Bezirk Suhl and Gerhard Müller, accountable for legal violations.

Subsequently, on 1 December 1989, the Erfurt Criminal Police initiated an investigation against Müller on suspicion of breach of trust through unjustified use of financial resources, focusing mainly on him having funneled public money into the construction of a luxurious hunting lodge near Luisenthal.

[1][2][12] Regarding legal matters, on 1 June 1990, Müller was charged,[13] and in 1992, he was convicted of incitement to breach of trust and fraud, resulting in an eight-month prison sentence, which was served with ten months of pretrial detention.

[2][1] Subsequently, on 3 November 1994, the Erfurt Regional Court sentenced him to eight months in prison, suspended on probation, for incitement to electoral fraud during the municipal elections in the German Democratic Republic (East Germany) in 1989.