The end-Permian mass extinction (EPME; 251.94 Ma) represents the most severe biocrisis in Earth's history. A key hypothesis links this marine mass extinction to the expansion of oceanic anoxia, yet the precise timing and tempo of ocean deoxygenation remain subjects of debate. Thallium isotopes have emerged as a sensitive paleoredox proxy capable of capturing rapid global redox changes due to their relatively short residence time in seawater and the high redox potential (Eh) associated with thallium cycling. In this study, we analyzed thallium isotopes from the marine Meishan and paralic Lengqinggou sections in the Tethys Ocean. We present highresolution epsilon 205Tl records from Meishan (ranging from -7.8 to -0.2), along with a second record from Lengqinggou section, both of which exhibit the same stratigraphic trend across the extinction interval. Geochemical signal preservation analysis suggests that the Lengqinggou section has been affected by non-redox processes, while the Meishan section preserves a robust primary seawater signal. Our new epsilon 205Tl data from Meishan provide evidence for the onset of deep ocean anoxia occurring considerably before the EPME-approximately 30 kyr earlier than suggested by other global proxy records (e.g., uranium isotopes). Thallium isotope mass balance modeling indicates a 60-86% decline in manganese oxide burial, consistent with widespread oxygen loss across the EPME. This early deoxygenation coincides with the onset of the composite marine richness collapse, while the delta 238U response peaks closer to the richness minimum. Thallium isotope values remain around -2 (approximating the upper continental crust value) in the post-EPME, indicating that widespread deep ocean anoxia persisted into the earliest Triassic. Thus, thallium isotope data reveal a more nuanced record of marine oxygen loss and its links to biological change, underscoring the role of oxygen depletion in past biological evolution.