Mohammed Rehman, 25, used the Twitter name “Silent Bomber” and asked users whether he should bomb a shopping centre or the London Underground train network.
Rehman used as his profile picture an image of the Islamic State (IS) group militant known as “Jihadi John”, believed killed earlier this year, and was said by prosecutors to have had a “keen interest” in IS.
He was arrested in May after posting a tweet saying: “Westfield shopping centre or London underground? Any advice would be greatly appreciated.”
That was accompanied by a link to an al Qaeda press release about the July 2005 bombings in which four suicide bombers targeted London’s transport system. Fifty-two people were killed.
The couple were accused of planning their attack around May 28.
Rehman and his wife Sana Ahmed Khan were found guilty by a jury at the Old Bailey in London, England’s central criminal court.
Police also seized more than 10 kilogrammes (22 pounds) of urea nitrate, which can be used to manufacture a large bomb, from their house and he filmed himself testing explosives in their back garden.
“The manufacture of a detonator would have taken no more than a couple of days and could have been done by him much quicker if he chose to,” prosecutor Tony Badenoch told the court.
While Rehman was responsible for creating the bomb, his wife funded his exploits and bought the chemicals, the Crown Prosecution Service said.
If detonated on the London Underground, the bomb they were preparing “would have caused multiple fatalities,” said the CPS.
“The intention to carry out some form of terrorism attack was clear,” Susan Hemming, head of the CPS counter terrorism division, said following the verdict.
“The pair had been very close to carrying out an attack. All they required was to purchase the chemicals to make a detonator.
“There is little doubt that, had Rehman and Ahmed Khan not been stopped when they were, they would have attempted to carry out an act of terrorism in London.”
The couple will be sentenced on Wednesday or Thursday, following mitigation hearings.