Husnain Rashid, of Nelson, Lancashire, admitted a string of terror offences in May which included using a Telegram chat group to call on supporters to target the four-year-old heir to the throne on October 13.
Prince George had started at Thomas’s Battersea, a private school in south-west London, a month earlier.
The 32-year-old also encouraged followers to poison ice cream and suggested which football stadiums terrorists could strike.
He was also planning his own online magazine offering tips for “lone-wolf attacks”.
On Friday Rashid appeared in Woolwich Crown Court where he was given a life sentence for each of three counts of engaging in conduct in preparation of terrorist acts.
He also admitted one count of encouraging terrorism and was sentenced to four and half years imprisonment, to run concurrently.
Sentencing Rashid, Judge Andrew Lees said: “The message was clear – you were providing the name and address of Prince George’s school, an image of Prince George’s school and the instruction or threat that Prince George and other members of the Royal family should be viewed as potential targets.”
Before Rashid pleaded guilty, the court heard that in the space of 18 months he sent in the region of 300,000 messages and posts on the highly encrypted communication app, Telegram.
Speaking after Rashid was sentenced Chief Superintendent Will Chatterton from Counter Terrorism Policing North West said Rashid was a “prolific” poster on Telegram and had spent 18 months locked away in a bedroom of his parents’ home where he “made links with known ISIS members and spent hours making online posters and propaganda encouraging would-be terrorists to carry out the most gruesome attacks”.
He added: “Rashid was developing his magazine, called Lone Mujahid, which could be described as a sort of e-toolkit for would-be lone-wolf attackers. He is a prolific and dangerous individual.
Chatterton said police beliveved that “was days away from travelling to Syria and are in no doubt that he would have continued to encourage others and promote his ideology”.
“Today the world is just that little bit safer,” the counter terrorism boss said of Rashid’s jailing.
Prosecutors said during Rashid’s trial that he was encouraging terrorism by posting a photograph of the prince at the school super-imposed with silhouettes of two masked jihad fighters.
The charges covered offences spanning from October 2016 to April this year.
In May, prosecutors told the court “the underlying message was clear” that “Prince George and other members of the royal family should be viewed as targets”.
“Even the royal family will not be left alone,” Rashid messaged the group, before sharing the school’s full address and postcode.
He added: “School starts early.”
Rashid’s list of targets were wide-ranging – including British Army bases, shopping centres, Jewish communities and government buildings, the court was told.
Prosecutors said on the first day of the trial: “His proposals were indiscriminate and made no distinction between adult and child, between members of fighting forces and civilians.”
Rashid also plotted to bring down an aircraft with lasers with a British terrorist in Syria, the court heard.
When police swooped on his house last November, Rashid “hurled” a phone containing a “treasure trove” of evidence over a wall and into an alleyway.
Rashid also posted a photograph of the Burmese ambassador to the UK, saying: “You know what to do”, urging others to “fight and spill the blood to the apes in your land” and calling for others to “start preparing tools and weapons/explosives”.