The 49-year-old from east London is now facing up to 10 years in prison
The extreme cleric has been convicted of inviting support for the terror group Islamic State in a series of lectures released on YouTube.
Security sources believe Choudary is linked to 500 British jihadis who have fled the UK to join the terrorist organisation in Syria and Iraq.
Until now, media agencies had been unable to report his conviction after a judge imposed a reporting ban due to a linked trial of Choudary's associates from Luton, who were also accused of encouraging support for IS.
The juries in the two cases were not aware that they were sitting on connected cases in the same building at the Old Bailey.
Speaking to Sky News the night before his conviction, Choudary insisted he was merely exercising his right to freedom of speech.
The 49-year-old from east London said: "If you look at my speeches, I have said the same thing for 20 years. For me, it is a matter of worship.
"If people are implementing the Sharia, then I cannot shy away from what the divine text says in relationship to that.
"If you cannot say when you believe in something and you cannot share that view, then you don't really have freedom to express yourself in this country."
The jury took less than three days to find Choudary and his co-accused Mizanur Rahman (32) unanimously guilty of inviting support for a terrorist organisation.
Choudary's conviction comes after a two-year, multimillion-euro investigation by Scotland Yard designed to bring to an end his two decades of extremist preaching.
The trial was the most crucial test of the limits of free speech in the UK in a decade, since the conviction of another hate preacher, Abu Hamza.
Choudary swore the oath of allegiance to the leader of IS after a meeting in an east London restaurant with a group of five followers.
It came just three days after Abu Bakr al Baghdadi declared he had re-established the ancient Islamic Caliphate.
Choudary and Rahman then delivered a series of lectures using religious passages to justify their support and urged others to follow their example.
One of the obligations both men talked about was to "make hijrah" - meaning to travel to the Islamic State - the court heard.
Choudary's speeches sometimes involved stirring his audience to fever pitch, as they shouted "Takbir!" and "Allahu Akbar!", meaning god is great.
He talked of violent jihad, quoting theologians and telling his audience: "We initiate the jihad against the kuffar [disbelievers] to make the name of Allah in the highest.
"Next time when your child is at school and the teacher asks, 'What is your ambition?', they should say, 'To dominate the whole world by Islam, including Britain, that is my ambition'."
Choudary shot to prominence after the 9/11 attacks in the United States, holding a news conference to praise Osama Bin Laden.
He did exactly the same four years later after the 7/7 bombings in London - but this time the attackers had links to his own extremist group.
He was also close friends with Michael Adebelajo, one of the killers of Fusilier Lee Rigby - and caused more outrage when he claimed the young soldier would be burning in hell.
But despite repeated horribly insensitive remarks, he always managed to stay on the right side of the law.
Richard Whittam QC, prosecuting, told the Old Bailey: "Terrorist organisations thrive and grow because people support them and that is what this case is about.
"Do not confuse that with the right of people to follow the religion of their choice or to proclaim support for the principle of an Islamic State or Caliphate."
The jury was told it was not illegal to think IS are a "good thing" nor to express those views to others, but it was unlawful to "invite support".
The prosecution said Choudary and Rahman sought to "validate the legitimacy" of both IS and Baghdadi, and in doing so emphasised the obligation on others to obey or provide support.
He will be sentenced at the Old Bailey in September.