Lin Ying-chang, 56, was convicted on charges of attempted murder and making an explosive without a permit over the July 2016 blast, which the Taipei district court said was a botched suicide attempt.
The explosion injured 24 people when it tore through the train as it pulled into a station.
"The defendant detonated the explosive device with the goal of committing suicide, as well as taking his revenge on society by means of killing innocent people. His motive was malicious," a court statement said.
He told the court he had struggled to find a job after being diagnosed with cancer and had ended up living in his car. He said he had also become estranged from his family.
But Lin believed that "society should be responsible for him", the court statement said.
The last major attack on Taipei's public transit was when a college student killed four people in a stabbing spree in 2014 on the metro, shocking the island and prompting a security overhaul.
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