Radical preacher Anjem Choudary jailed for five-and-a-half years
The 49-year-old was convicted at the Old Bailey after backing the group in an oath of allegiance published online.
Police say Choudary’s followers carried out attacks in the UK and abroad.
The judge, who described Choudary as calculating and dangerous, passed the same sentence on his confidant Mohammed Mizanur Rahman, 33.
Both men were also sentenced to a notification order lasting 15 years, which requires them to tell police if details such as their address change.
Choudary, of Ilford, east London, and Rahman, from Palmers Green, north London, were convicted last month of inviting support for IS – an offence contrary to section 12 of the Terrorism Act 2000 – between 29 June 2014 and 6 March 2015.
The trial heard the pair also used speeches to urge support for IS, which is also known as Daesh, after it declared a caliphate in the summer of 2014.