Climate change policies and the green energy transition have renewed colonial structures and injustices for Indigenous peoples in land-use conflicts, but not without resistance. This article explores epistemic controversies in a legal struggle concerning impacts from wind energy infrastructure on Southern Saami reindeer herding and culture in Norway. The article draws on courtroom ethnography and diverse written material concerning a court case between the wind energy company Fosen Vind DA and the Southern Saami reindeer herders in Fovsen Njaarke Sïjte. The findings show that the parties’ competing claims to truth rely on different knowledge systems and worldviews concerning what Southern Saami reindeer herding is an ought to be. However, beyond onto-epistemological struggles between the “Indigenous” and the “Western”, Fosen Vind DA and the Norwegian state strategically ignored all knowledges that threatened capitalist and green colonial interests. The Fosen case illustrates how Indigenous peoples can contest dominant knowledge regimes and colonial presumptions about their livelihoods, culture, and rights through the legal system. However, the Norwegian state’s reluctancy to respect the outcome of the Supreme Court verdict reveals that asymmetric power relations continue to pave the way for colonial dispossession of Saami landscapes, epistemes, and human rights in the green energy transition.