Father-of-four Syed Hoque, 37, of Stoke-on-Trent, smuggled Â£4,500 to help his nephew buy a gun, a court heard.
He and his "fixer", 28-year-old Mashoud Miah, from east London, were convicted of funding terrorism in December.
Hoque was handed a five-and-a-half year sentence at the Old Bailey, while Miah was jailed for two and a half years.
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The court heard Hoque received messages on WhatsApp from Mohammed Choudhury, his 26-year-old nephew who was fighting with a group affiliated to al-Qaeda, begging for money to buy a Dragunov sniper rifle.
He was then put in touch with Miah, a gas engineer who had travelled to and from Syria with Muslim community-led aid convoys in 2012 and 2013.
During the trial Hoque said he believed Syrian President Bashar Assad was a "tyrant" who was "killing indiscriminately" and his nephew had told him he was travelling to Syria for "humanitarian" reasons.
Lawrence McNulty QC, defending Hoque, said his client had "concern for the weak and the underprivileged", and claimed the UK government "has supported rebel groups" since 2005.
Judge John Bevan QC said Hoque acted like "the only sheriff in town", adding it was "unattractive" he was "prepared to sacrifice" his nephew.
Representing Miah, David Gottlieb said he "crossed the line and broke the law" because he had "seen the effects of the Assad regime".
However, Judge Bevan said the defendants had "sought to abuse the legitimate aid convoys which depend on integrity if they are to function properly".
"There is no such thing as noble-cause terrorism," he said.
Two British men who used aid convoys as cover to smuggle cash to al-Qaeda-backed extremists in Syria have been jailed.