Wiesner started her political career as a 13 year old, after having seen Al Gore's film An Inconvenient Truth. After realizing that the environmental movement was her major political issue she chose to join the green liberal Centre Party, where she began regional chairman for the youth wing.[4]
In the run-up to the 2019 European Parliament election, Wiesner was third on the Centre party list with a campaign slogan to bring "new energy to Europe" and wanting to increase the renewable energy in the union.[5] The Centre party won two places in the election and even though Wiesner received more than 20,683 votes,[6] it was not enough to reach over the threshold.[7]
2021–present: Member of the European Parliament
On 11 December 2020, it was announced that Wiesner was going to replace Fredrick Federley's seat in the European Parliament, after his resignation the same day.[8] At 28 years of age, she became Sweden’s youngest member of the European Parliament.[9]