The AfD on Tuesday became Germany's first far-right party to win the post of speaker in a state parliament since World War II, when its candidate was elected in an eastern region.
The Alternative for Germany (AfD) took nearly 44 percent of the vote last month in Saxony Anhalt state in the former communist East Germany, easily beating the centre-right CDU of unpopular Chancellor Friedrich Merz.
Newly elected state lawmakers gathered for the first time Tuesday in parliament in the state capital Magdeburg to elect a speaker, with the AfD's candidate Tobias Rausch winning 48 votes, with only 29 against and five abstentions.
Several hundred anti-AfD protesters gathered outside holding signs with slogans such as "Never again is now" in reference to Germany's Nazi past and reading out parts of the constitution which set out citizens' basic rights.
Sandy Gaertner, one of the organisers said that "critical voices of civil society... need to be loud", accusing the AfD of "hollowing out, stretching and even trampling on" the constitution.
The anti-immigration and Moscow-friendly AfD narrowly missed out on an absolute majority in the state vote, winning 39 out of 83 seats.
Five lawmakers from the small BSW, a left-wing party that nonetheless echoes the AfD's stances on Russia and immigration, had already said they would vote for Rausch, 35.
Tuesday's results mean that four other MPs voted for Rausch in the secret ballot, boding well for the party's hopes of forming a government in the state.
That would be another first in Germany's post-1945 politics.
The BSW's deputy leader Christian Leye defended the party's decision to vote for Rausch, saying the "firewall" erected by the other parties against co-operation with the AfD "is not working".
"We need a smarter way of dealing with the AfD and that means tackling the content of their programme instead of a firewall," Leye told the Politico site.
In his acceptance speech Rausch promised to "take different opinions seriously and to try to take decisions transparently".
Green MP Susan Sziborra-Seidlitz gave an impassioned speech after the vote voicing alarm at the result.
"Whoever has invested a representative of extremist and anti-constitutional party with this office will bear responsibility for the consequences," she said.
The AfD's leader in Saxony Anhalt, Ulrich Siegmund, has said he hopes to be elected as state premier in December, which would be another first for the party.
The BSW has so far not committed to backing Siegmund for the post, although according to local media the two parties have agreed to co-operate on issues such as a commission of inquiry into government policies during the coronavirus pandemic.
The AfD also came first in an election in the eastern state of Mecklenburg-Western Pomerania last month, although a coalition of left-wing parties is expected to continue governing.
In the city-state of Berlin, the Linke party notched up a victory as both Merz's CDU and the chancellor's junior coalition partners, the centre-left Social Democrats, slumped.
The results of all three regional elections have added to pressure on Merz, who took office in 2025 promising to sap the AfD's appeal by kickstarting Germany's spluttering economy and taking a tougher line on immigration.
But his coalition has instead been beset by disagreements over reforms while the AfD has surged, reaching 30 percent in the latest opinion polls, while the CDU/CSU continues to drift downwards as low as 17.5 percent.