Prosecutors had demanded that Shoko Asahara, 48, the former leader of the Aum Shinri Kyo (Supreme Truth Sect), be hanged for ordering the subway attack and a string of other crimes that killed another 15 people.
"I sentence the defendant to death," said Judge Shoji Ogawa after Asahara had stood to hear the verdict that concluded the eight-year trial.
Eight guards had to help him rise at the judge's order to stand.
The gassing, with its images of bodies lying across platforms and soldiers in gas masks sealing off Tokyo subway stations, stunned the Japanese public, accustomed to crime-free streets.
The cult's arsenal including the nerve gas sarin, first developed by the Nazis, raised concern worldwide about the ease of making biological and chemical weapons of mass destruction.
"These actions plunged Japan and the world into deep fear," Ogawa said in commenting on Asahara's crimes.
Japan's fears of terrorism have mounted since the September 2001 attacks in the US and the controversial dispatch this month of Japanese troops to help rebuild Iraq.
About 5500 people were injured, some permanently, when members of the doomsday cult released sarin in Tokyo rush-hour trains on 20 March, 1995.
Asahara, handcuffed and clad in a black sweatsuit, his once-flowing black locks and beard now cut short and flecked with grey, muttered and smiled as he was led into the court room.
The trial generated huge public
interest in Tokyo
Asahara, whose real name is Chizuo Matsumoto, had pleaded not guilty but never testified and has only made confusing remarks in the courtroom, including babbling English words.
In a statement that took hours to read, Judge Ogawa said Asahara had ordered the 1989 murder of anti-Aum lawyer Tsutsumi Sakamoto and his wife and child, and conspired in a 1994 sarin attack in central Japan that killed seven people and in the 1995 subway assault.
Rows of media photographers lined up outside the Tokyo District Court, where officials said 4658 people had tried to register for one of the 38 seats allocated to the public.
Tokyo police mobilised 400 officers throughout the capital and even organised a fake motorcade to divert media attention when Asahara was being transported to the court.
Survivors said even a death sentence for Asahara would not bring them relief, especially since the reason behind the crimes remained a mystery.
"This issue will absolutely never end. I don't think of this as providing closure at all," said Hiroyuki Nagaoka, who was targeted in a separate gas attack by Aum members in January 1995 when he was head of an anti-cult group.
Asahara set up the cult in 1987, mixing Buddhist and Hindu meditation with apocalyptic teachings to attract, at its peak, at least 10,000 members in Japan and overseas, among them graduates of some of the nation's elite universities.
The pudgy, nearly blind guru predicted that the US would attack Japan and turn it into a nuclear wasteland.
He also claimed to have travelled forward in time to 2006 and talked to people then about what World War Three had been like.
Asahara and other cult members ran for parliament in 1990 but won only a smattering of votes.
Commentators have speculated that Asahara, who came from a poor family and graduated from a high school for the blind, grew angry at society after that and led the cult down a murderous path.
After the elections, Aum set up a huge commune-like complex at the foot of Mount Fuji, where members not only studied his mystical teachings and practised bizarre rituals but built an arsenal of weapons including the sarin used in the subway attack.
The attack prompted the police - who came under fire for failing to prevent it - and the military to beef up their capability to deal with chemical and biological attacks.