Waheed Arafat Khan, Ibrahim Savant and Waheed Zaman were facing trial for a third time following hung juries in the first two trials.
The defendants were each facing a single charge of conspiracy to murder persons unknown.
The Home Secretary said: ‘I welcome the verdicts in which three people have been found guilty in one of the most significant terrorist plots the UK has ever seen. National security is our top priority and this result reflects the continued and serious threat we face.
‘I commend the efforts of the police, security services and the Crown Prosecution Service in bringing these individuals to justice.’
The head of the plot, Abdulla Ahmed Ali, had planned to target seven transatlantic airliners with a co-ordinated strike by suicide bombers. Ali and two other plotters were found guilty after a 2009 retrial.