Sahayb Abu, 27, bought an 18-inch sword, a knife, balaclavas and body armour online as he prepared to strike last summer.
MI5 and police were actively investigating him since March 2020 after concerns about his extremist mindset.
During their conversations, Abu claimed he wanted to be a successful rapper in the future.
In one of his songs, he refers to himself as a “straight ISIS supporter”, talks about “heads rolling on the ground”, and says “got my suicide vest, one click boom and I’ll see you later.”
Abu was eventually arrested on July 9 after speaking about guns to the undercover officer.
But when he was questioned during an interview by police, he denied any intention to commit a terrorist attack and said the items he had purchased were for display purposes and for use in parody “drill” music videos.
Despite this claim, a jury found him guilty of plotting terrorist acts after deliberating for more than 21 hours and he was jailed for life with a minimum term of 19 years at the Old Bailey.
Commander Richard Smith, head of the Met’s Counter Terrorism Command, said: “This is a prime example of how our officers and the security services are working together to keep people safe.”
He added: “Over several months, Abu sought to obtain weapons and the equipment needed to commit a terrorist attack. He is an extremely dangerous individual, but we were able to intervene and arrest him before he was able to carry out his attack.
“This investigation took place during the Covid-19 pandemic, but our focus on keeping the public safe from terrorism has not wavered during that time.”
His brother Muhamed Abu, 32, of Norwood, south London, was cleared of failing to tell authorities about the plot.