With Kyra Gantois and Adélaïde Charlier, De Wever became one of the leading figures in the School strike for climate movement in Belgium.

[3][4] Personal differences led to a fissure within the Belgian Youth for Climate movement, with the departure of co-founder Kyra Gantois in August 2019.

[5] De Wever made an appearance at the 2019 Pukkelpop music festival attempting to engage the audience to call attention to the climate issues.

This call angered some festival goers who harassed their group, hurled bottles of urine at them, and followed them back to their campsite, uttered death threats and destroyed their tent, forcing security to intervene.

[12][13][14] She received criticism for calling Gert Verhulst an "old white straight male", which prompted reply from the Belgian Secretary of State, Asylum and Immigration Sammy Mahdi who said: "Can we stop reducing a person's opinion to age, skin color, sexual orientation and gender?".