Lachit was youngest born to
Momai Tamuli Borbarua, a commoner who rose to the rank of
Borbarua under
Pratap Singha and Nang Lacheng Aaideu (). His sister was Pakhari Gabhoru, a queen to the Ahom kings
Jayadhwaj Singha and
Chakradhwaj Singha, and his niece was
Ramani Gabharu, the Ahom princess who was given to the Mughals as part of the
Treaty of Ghilajharighat. A few
Buranjis give some details on Lachit's life and education. He learnt the art of statecraft from his father and grew up instilled with a sense of loyalty to the king. He is said to have participated in battle against Mir Jumla's forces at Dikhaumukh and rose up the ranks of Ahom officialdom—
Ghora Barua,
Dulia Barua,
Simalugiria Phukan and
Dolakasharia Barua. Following the Chakradhwaj's preparations to retake Guwahati and on the eve of the march, Lachit was appointed the Borphukan (Ahom viceroy in the west) and the commander of the Ahom forces. As Borphukan, he worked to develop Lower Assam by organising new villages, instituting crafts classes for women and taking a census of the population. During this time, he received a letter mistakenly from
Kachar addressing him as the King of Lower Assam (
Narayan Raja), to which he took offence.
Guwahati campaign Lachit set up his base-camp at Kaliabar and then advanced on Guwahati in August 1667 in two divisions; and after a series of battles, finally retook Guwahati with the fall of Itakhuli in November 1667.
Death . A few Buranjis briefly describe Lachit's victory over the Mughal naval fleet, led by Ram Singh, in the
Battle of Saraighat. He died soon after in Kaliabor and was buried at
Teok in Jorhat in a
maidam, == Contemporary narratives ==