Josh Walker, from Bristol, fought alongside the Kurdish Militia and the YPG against Islamic extremists during a six-month stint.
He told the BBC that he “wouldn’t have forgiven himself” if he had not joined hundreds of volunteers who travelled to the war-torn country.
According to The Syrian Observatory for Human Rights more than 400 people joined the militia by 2015.
Mr Walker fought with fellow Brit 20-year-old Ryan Lock from Chichester, West Sussex, who died in December after "turning the gun on himself" to avoid being captured by terrorists.
He returned to the UK and was arrested at Gatwick Airport under the Terrorism Act, but was later released on bail.
He told the BBC's Inside Out programme that, despite bombing raids and mortar attacks which left him "terrified", he will "always be proud of what he did".
He added: "I hadn't gone out in a gung-ho manner but if I was under attack I was going to fight.
"All you can do is keep your head down and hope it stops," he said.
Mr Walker made his way to Syria after travelling from Bristol to Istanbul in Turkey, then to Iraq before reaching Rojava in Kurdish-held northern Syria.
The Foreign Office advises against all travel to Syria, adding there is a "high threat from terrorism" and a "very high threat of kidnapping" throughout the country.