Willem Holleeder's "life was determined by greed, lust for power and violence", judges said as they convicted the 61-year-old at a hearing in a secure court in Amsterdam dubbed "De Bunker."
Holleeder, nicknamed "The Nose" because of his most prominent facial feature, became a minor celebrity following the abduction of beer heir Freddy Heineken and his driver in 1983.
The burly ganglord appeared on television and was even known as the "huggable criminal" for posing for selfies with fans on Amsterdam's beer terraces.
But the public image masked the brutal reality of a gangland enforcer who ruthlessly wiped out anyone who threatened his position as king of the Amsterdam underworld.
He was found guilty of ordering five murders and one manslaughter.
In scenes reminiscent of Hollywood mob movies the Godfather and Goodfellas, he ordered the murder of Cor van Hout, his former friend and partner in crime in the Heineken abduction.
Van Hout was the father of the children of Holleeder's sister Sonja but was nevertheless gunned down outside an Amsterdam restaurant in 2003, after two earlier attempts on his life.
Holleeder -- who has been detained since 2014 -- was also convicted of ordering the murders of so-called "banker for the mob" Willem Endstra in Amsterdam in 2004, gangster John Mieremet in Thailand in 2005, building contractor Kees Houtman, also in 2005, and associate Thomas van der Bijl in 2006.
At the court, from which the public was banned due to security fears, judges said Holleeder "had an unscrupulous and indifferent attitude to life and death."
"His violence has led to close relatives only having the courage to testify when they, too, saw no other way out," they added.
"The court comes to the conclusion that there is a great risk of repeated violent criminal offences and that a life sentence is therefore appropriate."
Holleeder continues to deny the charges and will appeal against the life sentence, his lawyers said.
In a handwritten note tweeted by his defence counsel, Holleeder spoke of an "unprecedented media campaign' against him, adding: "I can see only that I have been right all the time."
Holleeder is further accused of ordering "hits" on his two sisters Sonja and Astrid after they testified against him. They were foiled after a fellow prisoner told police.
"He doesn't tolerate being crossed," Astrid, who wore a wire to record her brother's confessions and now lives in hiding, told Dutch newspaper NRC in 2016.
Astrid wrote a best-selling book called "Judas" about her brother, describing what she said were his rages and increasingly brutal and controlling behaviour.
The Heineken kidnapping is one of the country's best-known crime sagas and was turned into a movie starring Anthony Hopkins.
Freddy Heineken and his driver were released after three weeks in captivity following the payment of a ransom of 35 million Dutch guilders (15.8 million euros, $18 million today) was paid. Most of the money was never recovered.
Holleeder -- whose alcoholic father worked for the Heineken brewery in Amsterdam -- fled to France with van Hout but the pair were eventually arrested.
They were sentenced to 11 years in 1987 for the abduction and released five years later, after which they reportedly used the missing money from the Heineken job to build a criminal empire based on drugs and the Amsterdam sex trade.
Holleeder spent a further five years in jail for extortion from 2007 but emerged even more famous.