The Paleoproterozoic Bomdila orthogneisses exposed in the Arunachal Pradesh, NE Lesser Himalaya are medium- to coarse-grained pelite-derived leucogranites emplaced in the amphibolite-facies schistose rocks. The main pluton consists of two suites, i.e. two-mica granite and tourmaline-bearing granite. The chemical compositions are similar to those of other Himalayan leucogranites, being typical for melts generated through anatexis of upper crustal material. Trace element composition and the presence of pelitic enclaves suggest that Bomdila leucogranites formed by vapour-absent anatexis of metapelites (mica schists) similar to those exposed in the Bomdila area. Phase equilibria considerations and comparisons with experimental data indicate that the magmas for two-mica suite were generated by dehydration melting of biotite under water-undersaturated conditions at temperatures of >800°C and pressures less than 5 kbar, with tourmaline-bearing samples representing near minimum melt compositions formed under low-extent dehydration melting of muscovite. The high Rb and low Y+Nb concentrations of the granites are consistent with syn-collisional tectonic setting, which might have resulted in the emplacement of leucogranites during periods of crustal thickening. Thus the indicated syn-collisional tectonic setting of the granites has noteworthy implications by documenting a strong evidence for the existence of a Proterozoic orogenic event in the Lesser Himalaya.