Heidi Wesson, 33, went into labor two weeks early and gave birth to a daughter around 3 a.m. Sunday in the medical tent of the Pilton, England, festival following a performance by The Rolling Stones, The Sun reported Monday.
The mother and newborn, who has not yet been named, were transferred to a nearby hospital.
Wesson posted to Facebook she and the infant are doing "fine and fabulous."
"Thanks to everyone for looking after us," Wesson wrote. "We are over the moon and a little shattered ;-) xxx ps: sorry for interrupting your night off Nana, bloody love you xxx."
A Glastonbury spokesman congratulated the mother.
"We'd like to send our congratulations to the family. We look forward to welcoming them back in future years," he said. "We've had babies born here that are now grown-ups. They still come every year. That's a beautiful thing."