The heavily-pregnant woman boarded the regional train in Leipzig, Saxony, shortly before 6am, unaware that she was about to go into labour.
But as soon as the train pulled out of the station contractions set in. Passengers alerted staff who then made an announcement to see if there was a doctor or nurse on board, an eyewitness told Bild newspaper.
As no doctor was onboard, two passengers led the mother-to-be into a disabled toilet, where they delivered the baby as the train sped towards neighbouring Halle, where medics were waiting.
Both mother and baby were doing well at St Elisabeth's hospital, Bild said.
“We're deeply moved by the wonder that happened on our S-Bahn this morning,” head of Deutsche Bahn's south-east regional branch, Frank Klingenhöfer, told the Halle Spektrum news site.
“Because of the unusual situation we at Deutsche Bahn regional have decided to present the baby with a lifelong pass to travel in Saxony, Saxony Anhalt and Thuringia,” said Klingenhöfer.