Damon Smith, 20, from Rotherhithe in southeast London, left his device in the front carriage of a Jubilee Line tube train on a weekday morning in October last year.
Had the device worked, it would have exploded just as people were being ordered off the platform at North Greenwich tube station.
The device contained gunpowder and metal ball bearings, packed into a metal flask.
The timer – a cheap clock wired to a battery and lightbulb – failed to fully ignite the explosive mix.
Prosecution experts said that if the device had exploded it would have caused damage to the train and, at the very least, injuries to those in the tube carriage.
Smith had a keen interest in Islam, guns, explosives and gambling, and collected pictures of extremists, including Abdelhamid Abaaoud, the alleged mastermind of the 2015 Paris terror attacks.
The 20-year-old had previously printed off an al Qaeda article entitled ‘Make a bomb in the kitchen of your Mom’ and made notes in green ink before shredding the sheets of paper.