Choudary, 57, was convicted in Woolwich Crown Court on Tuesday of membership in a banned organisation, the radical Muslim group al-Muhajiroun, or ALM, and for drumming up support for the group.
ALM was outlawed by the British government in 2010 as a group involved in committing, preparing for or promoting terrorism.
"ALM's tentacles have spread across the world and have had a massive impact on public safety and security," Metropolitan Police Commander Dominic Murphy said.
"There are individuals that have conducted terrorist attacks or travelled for terrorist purposes as a result of Anjem Choudary's radicalising impact upon them."
Prosecutor Tom Little, who described Choudary as having a "warped and twisted mindset", said he had stepped in to lead ALM after Omar Bakri Muhammad, the group's founder, was imprisoned in Lebanon between 2014 and March 2023.
Choudary, who was previously convicted of supporting the Islamic State group, denied at trial that he promoted ALM through his lectures, saying ALM no longer existed.
Prosecutors said the group had operated under many names, including the New York-based Islamic Thinkers Society, which Choudary had spoken to.
The Islamic Thinkers Society was ALM's US branch, said New York Police Deputy Commissioner Rebecca Weiner, who called the case historic.
"It is usually the foot soldiers, the individuals who are brought into the network who go on to commit the attacks who are brought to justice," Weiner said.
"And it's rarely the leader, which is what makes this a particularly important moment."
Choudary was convicted with one of his followers, Khaled Hussein, who prosecutors said was a dedicated supporter of the group.
Hussein, 29, of Edmonton, Canada, was convicted of membership in a proscribed organisation.
The two were arrested a year ago after Hussein landed at Heathrow Airport.
Sentencing is scheduled for July 30.
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