Salem was convicted earlier in the month for the March 1995 killing of builder Pradeep Jain, who was shot outside his Mumbai home in a property dispute.
Salem, who is also a prime suspect in the 1993 Mumbai bombings, was arrested in Portugal in 2002.
He was extradited to India in 2005 and has been in prison since then.
There are at least another 25 cases of murder, extortion and kidnapping registered against him and he is also accused of terrorising Bollywood film stars and producers.
Indian authorities say Abu Salem, an Indian Muslim, is a key associate of crime lord Dawood Ibrahim, who is believed to be the mastermind behind the 1993 bombings which killed more than 250 people.
Salem fled India after the bombings with his companion and former Bollywood actress Monica Bedi.
The couple were arrested on an Interpol warrant and Portugal agreed to extradite Salem and Bedi after assurances from India that they would not face the death sentence.
The 47-year-old gangster is lodged in Taloja Central Jail in Raigad district near Mumbai.
A court in India's Mumbai city has sentenced gangster Abu Salem to life in prison for a 20-year-old murder.