Her father did military service in the National People's Army and subsequently worked as a truck driver and police officer.

[2] In 2001, Hennig began working for the Party of Democratic Socialism (PDS) parliamentary group as a research assistant for education and the media.

[6] In the 2009 Thurinigian state election, Hennig was re-elected to the Landtag, this time as member for the Erfurt II constituency; she defeated incumbent Christian Democratic Union of Germany (CDU) deputy Michael Panse to win the seat.

After Bodo Ramelow was elected Minister-President in December 2014, Hennig-Wellsow succeeded him as leader of the Left parliamentary group.

She has expressed preference for a R2G coalition with the SPD and Alliance 90/The Greens but stated that her primary goal is a federal government without the CDU/CSU.

She has also taken a more hostile attitude toward Russia than others in her party, including in regards to Russian actions in Ukraine and Syria, and the poisoning of Alexei Navalny.

She is also noted for her bold, sometimes aggressive tone; during the 2019 state election campaign, she coined the phrase "Bodo or barbarism!

[19] On one occasion during the 2020 Thuringian government crisis, Hennig-Wellsow responded to CDU demands with the message: "Our view remains: the first ballot has to pass with a democratic majority.

After Thomas Kemmerich (Free Democratic Party) was controversially elected Minister-President with the support of Alternative for Germany, the leaders of the parliamentary groups were invited to congratulate him and present him with a bouquet of flowers.

As the leader of the largest group, Hennig-Wellsow was the first in line; however, she refused to shake his hand, instead dropping the bouquet at his feet and walking away in protest.

[24] Hennig-Wellsow was widely criticized for an interview she conducted on 4 March 2021, during which she asserted that she was against the German military being involved in "combat missions" abroad but was unable to say how many active combat missions Germany was engaged in at that time and tried to appeal to a member of staff for assistance answering further questions about German military activity.

[25][26][27] Hennig-Wellsow received further criticism for her interview with Markus Lanz, aired on 31 March 2021, during which she struggled to answer basic facts about The Left's tax proposals.