[3][4] Kianni became interested in climate activism while in middle school in Tehran when one night the stars were obscured by smog.

"[5] She later joined Greta Thunberg's group, Fridays for Future, and took time off from school to support action on climate change.

[7][6] In November 2019, Kianni skipped school to join a group of protesters organized by Extinction Rebellion who intended to stage a week-long hunger strike and sit-in at the Washington, D.C., office of Speaker of the House Nancy Pelosi, demanding that she speak with them for an hour on camera about climate change.

[2][9] Kianni was not a member of XR, and only participated in the first day of the sit-in, but gave a prepared speech and interviews to the press, and continued the hunger strike remotely.

[19][20] In September 2021, Kianni was one of 4 co-chairs of the Youth4Climate event in Milan, preliminary to the 2021 United Nations Climate Change Conference or COP26.

[23] At COP26 itself, in November 2021 in Glasgow, Kianni spoke at several panels, and met with António Guterres, Secretary-General of the United Nations.

[25] At COP28, Kianni announced her We Wear Oil campaign, designed to draw attention to the contribution of fossil fuels used in fashion to the climate crisis.

[1] She wrote an article for MTV News for the 50th anniversary of Earth Day, which she helped coordinate,[33] and another in 2022 for The Washington Post about how she lives sustainably in college.

[34] In 2023, she partnered with Greta Thunberg and Vanessa Nakate to write a CNN editorial calling US President Joe Biden's endorsement of the Alaskan oil drilling Willow project a betrayal.

[13] She says she noticed informational content about climate change is either available only in English, or at best in Chinese and Spanish, making them inaccessible to speakers of other languages.

[58][34][59] Kianni received extensive media attention as an example of a teenager reacting to the social distancing measures related to the COVID-19 pandemic: CNN, Time magazine, and The Washington Post wrote about how she and her friends were moving personal interaction and even their physically cancelled senior prom to Zoom video chats and TikTok videos.