The reporting ban was lifted by Leeds Crown Court Tuesday.
A judge told him his actions could cause the ongoing trial to be re-run, costing "hundreds and hundreds of thousands of pounds".
Tommy Robinson is the founder of the English Defense League.
Robinson was outside Leeds Crown Court that day, hosting a Facebook live about a child grooming trial that was underway, one of a series of high-profile child grooming cases that the United Kingdom has seen over the last decade.
At court he admitted committing contempt of court by publishing information that could prejudice a trial. We believe not only must Justice be done; it must also be seen to be done and that is why this newspaper has been in court, covering that trial and will continue to do so, even though we may not be able to bring you details of it for some months. "Everyone understands the right to freedom of speech but there are responsibilities and obligations".
While sentencing Robinson, a judge warned that if he appeared at another court and risks "substantially derailing" a trial, he would jailed for breaking contempt of court laws, which aim to safeguard the judicial process and stop trials collapsing over fears the jury has been swayed before they have delivered a verdict.
Robinson rose to prominence in the United Kingdom as the founder of far-right group the English Defence League, before leaving in 2013.
His jail term can be revealed after media outlets successfully contested reporting restrictions imposed on the case last week.
Robinson's sentence follows a previous conviction on the same charge past year for which he received a suspended sentence that was still in force when he filmed his comments outside the court last week.
In the video, Robinson could be heard reading out defendants' names and the charges they were accused of-some of which were incorrect-as they arrived at the court.
He is active in the global far-right, writing and broadcasting for Canadian far-right channel Rebel Media and his arrest on Friday on suspicion of breaching the peace outside a court in the United Kingdom attracted tweets of protest by right-wing activists and commentators around the world.
Matthew Harding, defending, said his client felt "deep regret" over his actions.
At the time of his arrest, Robinson was reporting live on Facebook across from the courthouse. Robinson had been arrested multiple times before last week, for crimes including fraud and assault, according to Leeds Live, and Twitter has permanently banned him for claiming that Islam is murderous.
Robinson is under a "suspended sentence for committing contempt of court over a gang rape case heard in Canterbury previous year", according to the Independent.
It became known for its street marches and demonstrations in towns and cities before he quit the group in 2013.