Omicron has emerged as the most successful variant of SARS-CoV-2. In addition to mutations in Spike that mediate humoral immune escape, the Omicron-specific Envelope (E) T9I mutation has been associated with increased transmission fitness. However, the underlying mechanism remained unclear. Here, we demonstrate that the E T9I mutation confers resistance to autophagy. Rare Omicron patient isolates encoding the ancestral E T9 remain sensitive to autophagy. Conversely, introducing the E T9I mutation in recombinant 2020 SARS-CoV-2 renders it resistant to autophagy. Our data indicate that the E T9I mutation protects virions against lysosomal degradation. At the molecular level, the T9I mutation increases the localization of E at autophagic vesicles and promotes interaction with autophagy-associated proteins SNX12, STX12, TMEM87B, and ABCG2. Our results show that the E T9I mutation renders incoming virions resistant to autophagy, suggesting that evasion of this antiviral mechanism contributes to the efficient spread of Omicron.