The Delhi High Court found Sajjan Kumar 73 guilty of instigating mobs during the mass killings triggered by the death of Gandhi at the hands of her Sikh bodyguards.
At the time Kumar was an MP with the-ruling Congress party. He was cleared in 2013 but the High Court reversed the judgment on appeal from federal investigators.
Kumar was found guilty over a case involving the murder of five members of a Sikh family in New Delhi after key testimonies from eye witnesses.
A two judge bench sentenced Kumar for criminal conspiracy; promoting hatred and acting against communal harmony, the Press Trust of India and other local media reported.
“It is important to assure the victims that despite the challenges truth will prevail,” the court said, according to the NDTV news network. “The aftershock of those atrocities is still being felt.”
Kumar, who has been asked to surrender by the end of this month and he will have to spend the rest of his life behind bars.
Last month, another suspect Yashpal Singh was sentenced to death for murder and rioting.
The 1984 bloodshed erupted just hours after Indira Gandhi was shot dead at her residence in New Delhi. It lasted three days with Sikhs; raped and murdered and their homes and businesses burnt down.
Indira was killed over her decision to use military force to expel Sikh separatists from inside the Golden Temple, The Sikhism’s holiest shrine in the northern Indian city of Amritsar. Sikhs make up some two per cent of Hindu majority India’s population of 1.25 billion.
Critics blame Congress of turning a blind eye to the killings and the role of leaders such as Kumar and Jagdish Tytler. Kumar, Tytler and others have always deprived of of any wrongdoing.