His mother, Angie Blannin, said the 24-year-old was a "hero in my eyes".
She told the BBC: "He loved what he was doing there, he loved being a soldier. He had the courage of his convictions.
"He stuck by his convictions because he wanted to be there and he wanted to see the end of Raqqa and to see the end of the caliphate. That was a moment in history, and he wanted to be part of it."
Ozkan Ozdil, who also fought with Mr Holmes in Syria, told the BBC his friend had become well-known and respected among Kurdish fighting units.
He said: "Everybody knew Jac. By his third tour out there his Kurdish was fluent. We had a bit of a laugh that he was my Kurdish translator.
"He spoke so fondly about Rojava [the name given to the Kurdish region of north east Syria]. He was the reason that made me want to go."

Mr Holmes fought in operations to push IS out of key towns and villages including Tel Hamis, Manbij, Tabqa and Raqqa.
He always knew he could face arrest from UK authorities for fighting abroad, but had previously told the BBC "you just have to hope that our justice system works in the correct way".
During the battle for the IS stronghold of Raqqa, he became part of a four-man sniper unit made up of international fighters who, like him, had joined the conflict voluntarily.
In the "223 YPG Sniper Unit" Mr Holmes fought alongside three others from Spain, the US and Germany.