U.S. District Judge Garland Burrell Jr. gave the 55-year-old former mathematician the sentence called for by a plea agreement that resolved charges related to three deaths and the maimings of two scientists.
"The defendant committed unspeakable and monstrous crimes for which he shows utterly no remorse," Burrell said, adding that he feared Kaczynski would try to kill again if not closely watched.
Outside the courthouse, David Kaczynski, who first tipped authorities to the possibility his brother was the Unabomber, praised Mosser and the other victims for the courage it took to speak up in court.
Earlier in court, his brother complained that the government had lied about his commitment to the Unabomber's anti-technology philosophy.
Kaczynski began the hearing by walking to a podium at the center of the courtroom and saying that the government, in court papers filed last week, was "discrediting me personally."
But the wife of one of his victims had urged Burrell not to listen.
"Lock him so far down that when he dies he will be closer to hell," Susan Mosser said.
In the sentencing memorandum, the government quoted extensively from Kaczynski's journals, in which he wrote of a grinding hatred of people.
The Unabomber had demanded that his 30,000-word treatise on the evils of technology be published. But in his journals, the government said, Kaczynski scoffed at environmental ideals.
"I believe in nothing," Kaczynski wrote. "I don't even believe in the cult of nature-worshipers or wilderness-worshipers. I am perfectly ready to litter in parts of the woods that are of no use to me."
Of his killings, Kaczynski wrote: "My motive for doing what I am going to do is simply personal revenge."
But speaking in a high-pitched voice, Kaczynski said Monday that the sentencing memo contained "false statements, misleading statements."
"By discrediting me personally, they hope to discredit my political ideas," he said.
Kaczynski asked people "to reserve their judgment about me and the Unabom case until I have a chance to respond."
He said he would further reply to the government in writing.
As Kaczynski began to speak, the family of the last Unabom victim to die, Sacramento timber lobbyist Gilbert Murray, stood up and walked out of the courtrooen masse.
The first victim to speak was Mosser, the wife of a New Jersey advertising executive killed by a package bomb.
She ticked off a list of household items - batteries, razor blades, pipes, nails - that in the Unabomber's hands became deadly weapons.
"Hold it in your hand when it is exploding and you have unbearable pain," she said.
She told how her then-15-month-old daughter had watched her father bleed. "No, no, no, not my Daddy!" Kelly Mosser had said.
Speaking above occasional sobs in the courtroom, Mosser added: "Make this sentence bulletproof - bombproof, if you will. Don't let him murder justice the way he murdered my husband."
Another Unabom victim, geneticist Dr. Charles Epstein, scoffed at Kaczynski's claim of the moral high ground. Kaczynski must not have believed too strongly in his anti-technology campaign, if he was unwilling to risk the death penalty by going to trial, he said.
"You saved your own neck. But you did everything, and more, and you did it in cold blood," Epstein said.
Kaczynski, a 55-year-old former math professor, agreed in January to a plea bargain that calls for him to be sentenced to life in prison. The agreement came only after U.S. District Judge Garland Burrell Jr. refused to allow Kaczynski to represent himself.
Kaczynski will likely be sent to a high-security federal prison, possibly in Lompoc or in Colorado.
As part of the plea bargain, Kaczynski acknowledged responsibility for all 16 Unabomber attacks between 1978 and 1995 that killed three people and injured 23 others.