The present study investigates the novel occurrence of rare garnet-aluminosilicate-bearing metapelitic enclaves from the Western Lohit Plutonic Complex in the Dibang Valley, Arunachal Pradesh, Northeastern India. Textural, mineralogical, thermobarometric and phase equilibrium modelling analyses reveal a complex polymetamorphic evolution characterized by two distinct stages. The first stage corresponds to a pre-Himalayan low-pressure, high-temperature event likely linked to Cretaceous magmatism, evidenced by relict andalusite porphyroblasts. The second stage reflects Barrovian-type Himalayan metamorphism associated with India-Asia collision, marked by peak assemblages of garnet, kyanite and melt formed near the solidus. Thermobarometric studies estimate near-peak metamorphic conditions at approximately 650 ± 25 °C and 7–9 kbar. Consistently, Pressure-temperature phase equilibrium modelling indicates that garnet core compositions record an initial metamorphic event at lower pressure (∼5.5 kbar) and temperature (∼550 °C), reflecting prograde burial prior to peak conditions. Peak metamorphic conditions, constrained by pressure-temperature phase equilibrium modelling, are estimated at approximately 670 °C and 8.5 kbar. Microstructural observations indicate muscovite-dehydration melting is the primary mechanism for incipient melt generation in the studied metapelite, with the melt largely retained within the rock. Ti-in-biotite thermometry reveals cooling temperatures of 560–590 °C during final exhumation. The rocks experienced a clockwise P–T path involving prograde burial, near-isothermal decompression and retrograde cooling, consistent with thrust duplexing and exhumation along the Lohit thrust shear zone. These findings provide new constraints on the metamorphic evolution and partial melting processes during Himalayan orogenesis in the northern Indo-Burma region.