During his time as a student, he became active in politics, and in 1979 he was named the president of the
All Assam Students’ Union (AASU), an influential organization in the state. That year the AASU embarked on a popular agitation against illegal immigrants from
Bangladesh that lasted until 1985. The movement, spearheaded by Mahanta, made him from being the leader of a student organization to becoming an influential politician. He was a major factor in the formation of the
AGP in October 1985 and was elected the party's first president. Mahanta was first elected to the
Assembly in
1985 for
Nowgong. Mahanta next was elected to the
Assembly in 1991 for
Barhampur. He defeated the
Indian National Congress candidate, Ramesh Chandra Phukan, by 17333 votes. He continued to represent
Barhampur in 1996, 2001 2006,
2011 and
2016. On 4 September 2010 he was again unanimously elected as the
Leader of Opposition in the
Assam Legislative Assembly. On 21 October 2013, representatives from eleven political parties of the North-east region met to form a new political front, the
North-East Regional Political Front (NERPF), to protect the interests of the region's people. Mahanta was appointed the front's chief adviser. On 14 July 2014 he resigned as president of
Asom Gana Parishad after its failure to get any seat in the
2014 Lok Sabha elections.
Chief Ministership AGP candidates secured a notable victory in December 1985, Mahanta who was one of those people, became the
Chief Minister, he became the youngest person in the
country to hold such a high office. His first administration, however, was beset by allegations of corruption and problems of escalating violence linked to the
United Liberation Front of Assam (a militant separatist group in the state). In 1990 the authorities in New Delhi dismissed the AGP government and took
direct rule of the state. A split in the party in 1991 and voter dissatisfaction with its performance in its first administration led to a poor performance for the party in the 1991 assembly elections. Following an AGP resurgence in the 1996 state assembly elections, Mahanta became the
chief minister for a second time. That tenure became highly controversial, especially after the revelation of a counterinsurgency strategy that allegedly was under the direction of Mahanta. In June 1997 the ULFA staged an attack on Mahanta, after which the police coerced ULFA cadres who had surrendered to the authorities to kill family members of active insurgents. An official commission that later was to investigate the killings and it concluded in 2007 that Mahanta was directly responsible for the policy. Also during his second administration, Mahanta was alleged to have been involved in a corruption scandal involving fraudulent letters of credit and avoided prosecution only through the intervention of the governor of Assam. Investigation of the matter was reopened in 2010. The 2001 elections were terrible for the
AGP as they only won 20 seats. On top of that, it was alleged that Mahanta had had an extramarital affair, he subsequently was ousted as president. Despite the allegations of secret killings he organized against families of ULFA members, documented in the report by the Saikia Commission to the Assam Assembly, Mahanta was missed from political leadership in the state. He was reinducted into the AGP after the AGP (Progressive) was dissolved during the presidency of
Chandra Mohan Patowary, and regained a prominent position in the party. In a 2010 interview on
NDTV's
Walk the Talk with
Shekhar Gupta, editor-in-chief of
The Indian Express, Mahanta said: "For the sake of the integrity and security of
India, we are ready to take any blame. If the insurgent groups attack our forces, then they (the security forces) must have the right to respond. However, the charge against me on extra judicial killings of the ULFA sympathisers is to malign my image." In the same interview, he said that unknown agencies of the
Congress Party had conspired in massacres during the
Assam Movement in the early eighties. == Personal life ==