While claiming benefits, the married father-of-five spoke “contemptuously” about the democracy in which he was born and “happily” relished the idea of the Islamic flag flying over 10 Downing Street.
Despite being a leading figure in the banned group al-Muhajiroun (ALM), and with a series of former supporters going on to be convicted of terrorism, Choudary had stayed on the right side of the law for two decades.
But in the summer of 2014, he “crossed the line” and backed IS in a series of talks posted on YouTube, and recognised a caliphate - a symbolic Islamic state - had been created under its leader.
Choudary, 49, from Ilford, and Mohammed Mizanur Rahman, 33, from Whitechapel, east London were found guilty of inviting support for IS and each sentenced to five-and-a-half years in prison.
Supporters in the public gallery of the Old Bailey courtroom shouted “Allahu Akbar” as Choudary was sent down to begin his sentence.
Choudary’s jail term could be served in solitary confinement to stop him radicalising inmates.
Sentencing, Mr Justice Holroyde said the men had shown “contempt for the values of the democracy in which we live” and failed to denounce the appalling violence of IS.
In one of the speeches, which would have been heard by impressionable people, he had referred “happily to the prospect of the flag of Islam flying over 10 Downing Street and the White House”, the judge said.
He described Rahman as a “hothead” while Choudary was more “calculating” and the more experienced, although both were dangerous and lacking in remorse.
The judge said: “At no point did either of you say anything to condemn the violent means by which ISIS claimed to have established a caliphate.
“In fact, none of the many speeches which the jury heard contains any criticism by either of you of any of the violent actions of Isis or its supporters.
“On the contrary, each of you was invariably able to find a way of justifying their most appalling acts.”