He was 53. Gamlin was suffering from liver thrombosis when he passed away last night.
He is survived by his wife, three daughters and a son.
His body will be flown to Aalo in West Siang district of Arunachal on Tuesday, they said.
Born on April 16 in 1961 at Aalo, Gamlin studied at Sainik School in Goalpara in Assam and graduated in History from St Stephen's College in Delhi. He obtained his law degree from Campus Law Centre, University of Delhi in 1984. Later, he practised as a lawyer in Dibrugarh.
He was President of the All Arunachal Pradesh Students Union (AAPSU) for three years from 1981.
Although Gamlin first joined the People's Party of Arunachal (PPA), he switched over to Congress and became a member of the Lok Sabha from 1999-2004.
In 2004, he was elected to the state Assembly and became Home Minister in the Gegong Apang ministry.
In 2009, he became Power Minister in the Dorjee Khandu government.
On May 5, 2011, Gamlin became the chief minister of Arunachal Pradesh after the death of Dorjee Khandu in a chopper accident.
His six-month-long chief ministerial tenure came to an end on October 31, 2011 after he resigned from the post following political upheaval in the state.
Gamlin was also elected to the Assembly this year.