Khalid Ali, 28, from North London, has been convicted of planning a terror attack in Westminster and making bombs for the Taliban.
Ali was arrested on April 27, 2017 in Parliament Street, where he was caught carrying three knives.
Prosecutors said Ali, from Edmonton, had planned a “murderous attack” on politicians and police.
In a police interview, Ali said he wanted to deliver a “message” to British authorities, but claimed the knives were for protection.
An Old Bailey jury convicted him of preparing an act of terrorism in the UK and two counts of possessing an explosive substance with intent. He will be sentenced on July 20.
On April 22 last year – one month after the Westminster terror attack – Ali was caught on CCTV walking past the MI6 building at Vauxhall Cross, as well as Westminster Bridge, the Houses of Parliament and Whitehall.
Five days later, his mother called police and said she had found four knives in his bedroom.
Police swooped in to arrest him just metres from Downing Street later that day.
Ali had spent several years in Afghanistan, and when asked by British police whether he had returned to the UK for jihad, he replied: “Jihad is what we do. We are Mujahideen.”
Prosecutor Brian Altman QC had told the jury that Ali planned a “deadly terror attack at the very heart of this country’s democracy by killing a police officer, a member of the military or even a parliamentarian”.
Ali travelled to Afghanistan in 2011 and spent five years making bombs to attack occupation troops.
During questioning after his arrest, Ali admitted fighting British soldiers in Afghanistan, but refused to say whether he had killed any.
In a police interview shown during the trial, Ali also said he had detonated more than 300 bombs.
The court heard how his fingerprints were found on component parts of explosive devices that were handed in to US forces in Afghanistan in 2012.
Police said Ali had been in a “Taliban training camp affiliated to al-Qaeda where, for several years, he helped terrorists make hundreds of bombs capable of mass murder”.