Anna Campbell was killed last week in the Afrin enclave, said Nisrin Abdallah, a spokeswoman for the Kurdish Women's Protection Units (YPJ).
"She died on March 15, 2018 in Turkish shelling" on frontlines around Afrin city, Abdallah told AFP, adding that Campbell was 27 at the time of her death.
"We learned of her death yesterday and communicated with her parents," she said, confirming that Campbell was from Lewes in East Sussex.
Ankara and allied Syrian rebels began their assault on the Afrin region on January 20, seizing most of the canton before capturing its urban centre on Sunday.
They swept into the city after the fighters from the YPJ and its male counterpart, the People's Protection Units (YPG), appeared to withdraw.
Abdallah said Campbell joined the YPJ in May 2017 but had not been deployed to the front line until this month.
"After the attack on Afrin, she insisted on being sent there," Abdallah said.
"We discussed with her a lot, but she gave us an ultimatum: either I quit the revolution or I go to Afrin," she added.
Hundreds of foreign fighters have joined the YPG and YPJ in Syria, with many saying they wanted to back a "revolution" for participatory democracy and women's rights.
Most have fought alongside the Kurdish militia in its battle against the Islamic State jihadist group.
British fighter Jac Holmes, from Bournemouth in southern England, was killed in IS's de facto capital Raqa in October, just days after Kurdish-led forces ousted the jihadists from the city.
At least two other foreign fighters have been killed in the Afrin assault, according to the YPG.
French national Olivier Francois Jean Le Clainche, 41, and Spanish national Samuel Prada Leon, 25, were killed fighting in the Afrin enclave in February.
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