Akayed Ullah, 28, set off the bomb during morning rush hour last December, causing himself serious burns but only lightly injuring five others.
Prosecutors said he told investigators he had done it on behalf of the militant Islamic State group (IS).
It was described in court as a "lone wolf" terrorist attack.
Ullah targeted an underground passageway near the Port Authority bus terminal in Manhattan - the busiest in the world - on 11 December 2017.
His defence team argued that he had only wanted to kill himself in the attack. Ullah denied the charges in January.
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