Since 1985 Althaus has been a member of the
CDU, remaining with the party as it transformed itself from a loyal supporter of the GDR's ruling
Socialist Unity Party of Germany (SED) to a loyal supporter of the West German party of the same name with which it merged in 1990 shortly after
German reunification. In 2000 he became chairman of the
CDU in Thuringia. Since 1990 he has been a member of the Thuringian
Landtag. In 1992 he became a member of
Bernhard Vogel's cabinet as State Minister of Cultural Affairs and Education. On 5 June 2003 Althaus was elected
Minister President of Thuringia; he succeeded Bernhard Vogel, who had resigned for reasons of age. As Minister-President he served as
President of the
Bundesrat in 2003/04. Althaus was also part of the
CDU/CSU team in the negotiations with the SPD on a coalition agreement following the
2005 federal elections, which paved the way to the formation of
Chancellor Angela Merkel’s
first government. After the
Thuringia elections of 2009, where the CDU went from having an absolute majority to not even having enough seats to form a majority coalition with the
FDP, Althaus resigned as Minister-President and as chairman of the CDU in Thuringia. ==Later career==