Kim Dae-Han, a taxi driver with a history of mental illness, was spared the death penalty sought by the prosecution because of his condition and remorse for causing the deaths and leaving 147 people injured, according to court officials.
Relatives of the victims reacted angrily at the verdict, demanding the death penalty.
Kim, 56, spread petrol in a crowded subway car and set it alight before jumping out of the train at a station on 18 February in Taegu, 320 km southeast of the capital Seoul.
The court also sentenced the engineers of two subway trains which burned and six other Taegu subway employees to jail terms ranging from 18 months to five years for negligence in one of South Korea’s worst ever transport disasters.
Subway officials have been accused of failing to respond swiftly to the danger of the fire by evacuating passengers promptly.
The blaze prompted Seoul to double this year’s budget for subway fire prevention to some $20 million, which will be used for buying heat resistant suits, special vehicles to extract smoke from underground facilities and vision-aid lanterns that can allow the users to see in smoke-filled areas.