Location: South India
Size: 1-2 cm
Precise identification of insects requires use of microscopic lens and an immobile specimen.
I have neither of those here; also, my reference material is focused on North American species. Nevertheless, with what I have available to me, it is most likely a member of order Hemiptera, family Alydidae:
Alydidae are mostly active during the day, so your specimen was probably resting and saw a nearby artificial source of light. They use their piercing mouth-parts to suck the juices out of herbaceous seeds. Unless yours was discovered in a heavily urbanized area, I would venture that this one feeds off nearby grasses and trees.