British cleric Anjem Choudary, who has long been accused of radicalising young Muslims, was facing jail on Tuesday after being convicted of encouraging support for the Islamic State group.
The 49-year-old Choudary and co-defendant Mohammed Mizanur Rahman, 33, used a series of talks posted on YouTube to invite backing for the group, and pledged their allegiance to IS leader Abu Bakr al-Baghdadi.
They were convicted of support for a proscribed terrorist organisation following a trial in London last month and remain in custody.
Legal restrictions were placed on the verdict being made public until now.
Choudary is the former head in Britain of Islam4UK or al-Muhajiroun, a now banned group co-founded by Omar Bakri Muhammad that called for Islamic law in Britain.
But for two decades the former lawyer, who is of Pakistani descent, managed to stay on the right side of the law.
Among those radicalised by Muhajiroun were the suicide bombers who killed 52 people on London's public transport system in 2005, and the men who murdered soldier Lee Rigby in the capital in 2013, police say.
"These men have stayed just within the law for many years," Commander Dean Haydon, head of counter-terrorism at London's Metropolitan Police, said of Choudary and Rahman.
"But there is no one within the counter-terrorism world that has any doubts of the influence that they have had, the hate they have spread and the people that they have encouraged to join terrorist organisations."
He said the oath of allegiance made in July 2014 was a "turning point", giving police the evidence they needed to prove that the men supported the Islamic State group.
Both men will be sentenced on September 6.
"This has been a significant prosecution in our fight against terrorism and we will now be working with communities to ensure that they are not replaced by others spreading hate," Haydon said in a statement.
