Rahman was encouraged to carry out his plans by his uncle, who had travelled to Syria and was killed in a drone strike.
According to special services, 20-year-old Naimur Rahman planned to blow up an improvised explosive device in Downing street, to break into the Prime Minister's office and kill the there may.
Image: A suicide vest belonging to Naa'imur Zakariyah Rahman.
A jury convicted him at the Old Bailey courthouse in London.
Rahman earlier admitted helping his friend Mohammad Aqib Imran, 22, join the Islamic State group in Syria by recording a sponsorship video.More news: Amazon set to challenge Apple with $900-bn market cap
His plot was discovered after he contacted an Federal Bureau of Investigation agent posing as an IS official online.
Imran was found guilty of having a terrorist handbook after 13 hours of deliberations by the jury, which on Wednesday night was still considering a charge against him of preparing terrorist acts overseas.
Officers became concerned about potentially extremist views after examining his mobile phone. "I want to attempt to kill Theresa May", he is reported to have told the undercover intelligence officers.
The jury is still considering a charge against Imran of preparing terrorist acts overseas.
"There are lorries here with big gas tankers, if a brother can drive it next to Parliament I will bomb".More news: Russian warship carrying £100BILLION worth of GOLD found off South Korea
The British prime minister stated that she "clearly and unequivocally" decries the policy, which has seen thousands of children forcibly separated from their parents at the Mexican border. I can't mess up.
In November 28 a year ago, the officer handed back Rahman's rucksack and coat - now packed with dummy explosives - and replica pepper spray.
A "full frontal assault" with a knife and bomb was to take place on November 28, last year, the Old Bailey heard.
Two days later, he bought a rucksack from Argos before meeting an undercover officer in Brixton for it to be fitted with explosives.
The terrorist was preparing a terrorist attack in the United Kingdom for two years.More news: Mark Wahlberg launching Chevy dealership in Ohio
Details of messages sent on the Telegram app by Rahman to a fake Isis member were read out in court.