Kahr joined the Communist Party in 1983. From 1985, she was employed in the KPÖ district management in Graz. She was elected to the city council in 1993, and since 1998 she has chaired the KPÖ council group. In 2003–4 she was deputy federal chairwoman of the KPÖ. She was campaign manager for the party in the
2005 Styrian state election, which saw the KPÖ become the third-largest party and win seats in the
Landtag for the first time in 35 years. After the 2005 state election, popular local KPÖ leader left the city council to focus on state politics. Kahr succeeded him as the face of the Graz KPÖ, and replaced him as councillor for housing, a position she held until 2017. The 2008 municipal election saw the party lose 6 of their 12 seats and slide to fourth place. However, it recovered in the following years and, under Kahr's leadership, became the second-largest party in Graz with 20% of the vote in the 2012 election, an unprecedented result. After the resignation of vice mayor of the
Social Democratic Party of Austria in 2016, Kahr was elected as her successor. She was confirmed by the Landtag with 38 of 46 votes. Kahr again headed the KPÖ list in the 2017 local election and maintained her party's performance at around 20%. After the election, she lost her housing portfolio and was instead appointed councillor for transport.
2021 municipal election Kahr led the KPÖ for a third time in the
2021 Graz local election. Despite opinion polling suggesting a victory for the ruling
Austrian People's Party (ÖVP), the KPÖ became the largest party with 28.8% of votes and 15 seats, making Kahr the most likely candidate for mayor of the city. After the election, the KPÖ entered into discussions with the
Greens and
SPÖ. The three parties agreed to form a
coalition government, with the KPÖ holding three city councillors and the Greens one, while the SPÖ take over a number of committees in the city council. Kahr was elected mayor by the Gemeinderat on 17 November, winning 28 out of 46 votes. She became the first female mayor of Graz and first communist mayor of an Austrian city. ==Political views and activity==