<p>Ferroptosis, an iron-dependent form of oxidative cell death driven by uncontrolled lipid peroxidation, has been increasingly implicated in neurodegeneration. However, its involvement and the underlying regulatory mechanism in <i>C9orf72</i>-linked amyotrophic lateral sclerosis (ALS), the most common genetic form of the disease, remain incompletely understood. Here, we show that the arginine-rich dipeptide repeat protein poly-GR promotes ferroptosis-associated molecular and biochemical features in motor neuron-like NSC34 cells. Poly-GR expression significantly increased lipid peroxidation, intracellular ferrous iron, and reactive oxygen species, indicating a cellular environment permissive for ferroptotic vulnerability. Mechanistically, poly-GR suppresses the Nrf2/Slc7a11 antioxidant defense axis by reducing Nrf2 nuclear localization and its occupancy at the Slc7a11 promoter, resulting in decreased Slc7a11 transcription. Restoration of Nrf2 or Slc7a11 expression attenuated lipid peroxidation and oxidative stress, while the iron chelator deferiprone effectively reduced Fe²⁺ accumulation and ferroptosis-associated injury. Functionally, poly-GR sensitized neuronal cells to erastin-induced ferroptotic stress-associated cell death, an effect reversed by Nrf2 or Slc7a11 overexpression and iron chelation. Together, these findings indicate that poly-GR disrupts redox homeostasis and iron metabolism to increase susceptibility to ferroptosis, highlighting the Nrf2/Slc7a11 pathway and labile iron regulation as potential therapeutic targets in <i>C9orf72</i>-associated ALS.</p>