The woman was running in the Oberföhring area of the park at some time between 7.30pm and 8.20pm when the attack happened, police report.
The English Garden is a park which stretches through northern Munich into the town centre, following the bank of the Isar river.
The woman lost consciousness during the assault. When she came to she found herself lying away from the path. She then went to a nearby restaurant where she was picked up by police and emergency services.
Due to the wounds she had suffered, she was then brought to hospital.
Police say that the current state of their investigation leads them to believe the woman was sexually assaulted.
The murder commission have now taken over the enquiry due to the severity of the woman's injuries. She is not however in a life-threatening situation.
Police say they are withholding further information for the sake of the investigation.
The attacker is described as male, 40 to 50 years old and wearing dark jogging clothes and a bobble hat.