The Green party's Ganserer is believed to be the first transgender person in Germany to hold a regional or national MP's seat, or to change their gender while in office.
Just a few weeks after coming out on social media to a burst of publicity, the 41-year-old will make a first appearance before the press Monday to discuss her change of identity.
Long a laggard on social issues, some abrupt changes have taken place in Germany in recent years.
Parliament legislated last month for a third gender on birth certificates after a Constitutional Court decision that the documents must respect intersex people.
And in summer 2017, MPs pushed through gay marriage after Chancellor Angela Merkel said she would not whip her party on the subject.
While Ganserer won her Bavarian parliament seat in October, in the United States Democratic party candidate Christine Hallquist recently failed in her bid to become the first transgender woman governor in Vermont.
'Madam regional MP'
“I am a woman with every fiber of my body and now Madam regional MP as well,” Ganserer posted on her Facebook account in early January, announcing her intention to sit in parliament as a woman.
She received lots of congratulations from well-wishers.
Just a few weeks ago, Ganserer had said both Markus and Tessa remained a part of her. But from now on she hopes to live as a female politician, wife and mother of two children.
While Bavaria is a strongly conservative and mostly Catholic region, the president of the regional parliament Ilse Aigner of the Christian Social Union (CSU) backed the change.
“Mrs Ganserer has taken a very brave and highly personal decision,” Aigner said.
The CSU usually takes very conservative positions on social questions and opposed the federal gay marriage law.
“Our male colleague is becoming a female colleague, that should not be a problem in this house,” Aigner said in a public statement after speaking with Ganserer.
“A person's personality is always more important than their gender.”
At the first plenary session of the year from January 23rd, the Greens party MP — first elected in 2013 and reelected last October — will be registered as a woman.
Das Leben als Markus Ganserer war nicht schlecht .
Aber ich bin Tessa Ganserer und werde jetzt endlich auch so leben. https://t.co/7F4nf1jK5b
— Tessa Ganserer (@GansGruen) January 4, 2019
“Life as Markus Ganserer was not bad. But I am Tessa Ganserer and I will finally live like this,” said Ganserer on Twitter.
'Getting used to it'
Among fellow MPs, “many definitely still have to get used to it,” Aigner said.
One member of the pro-business FDP cried “what are you playing at here? A drag queen?” when he first saw Ganserer in a long blonde wig and makeup in the Munich chamber, daily Süddeutsche Zeitung (SZ) reported.
As for her official identity papers, Ganserer has a little longer to wait. In late November, she received a medical certificate from a psychiatrist confirming she is transgender.
German law requires two medical opinions to back a name change in the official register. Securing that step “meant getting my real birth certificate to me”, Ganserer told the SZ.
While she has made little public comment, she told the paper that she “discovered” herself as a woman around 10 years ago when looking in the mirror wearing a dress.
Since then, she has picked her way through different roles: as man, father, husband, woman, wife, and mother.
Now, her doubts are so far gone that she has told her sons, 11 and 6, that “from now on I will always be like this”.
“Children don't have prejudices. If you present the world to them in a friendly way, they will accept it as it is,” Ganserer said.
She doesn't plan to undergo any medical procedures, but to mark the definitive arrival of Tessa, Ganserer took a major step: she packed all her ties, shirts and suit jackets into bags and gave them away.