Imran Khawaja, who has close ties to IS 'executioner' Jihadi John, had appeared in videos posted online for Islamic State's propagandist arm, the Rayat al-Tawheed (RAT), including posing with severed heads and dead fighters.
Last month, he had admitted preparing for acts of terrorism, attending a camp, receiving training and possessing firearms.
Khawaja, a bodybuilder, was arrested in Dover last June after faking his death and trying to return to the UK undetected.
His cousin, Tahir Bhatti, was jailed for 21 months. He will serve half of his sentence. Bhatti had driven to Serbia to collect Khawaja and bring him back to the UK.
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Another man, Asim Ali, who provided his friend Khawaja with funds - was also given 21 months in prison.
Khawaja's counsel Henry Blaxland told the court his client had a very low IQ and had been "indoctrinated" in the months before he fled for Syria, in January 2014.
The judge also dismissed Khawaja's claim that he came home to see his family and regretted his actions, the BBC reported.
The judge said: "It is clear in the last few years you have been showing an increasing interest in Islamic jihadist material.
"You took part in the production of films designed to promote the Islamic State cause and encouraging UK Muslims to join you in jihad.
"Your interest was sufficiently profound for you to travel to Syria to train for jihad.
Khawaja showed no emotion as he was led from the court.