Police were called to Elm Grove following the collision between the 25-year-old pedestrian and a Renault Twingo.
The incident happened outside popular pub the One Eyed Dog on Friday night.
Police closed part of the road while the woman was treated by paramedics.
Officers were called at 10.46pm.
A spokeswoman for Hampshire Police said the woman had serious injuries and was taken to Queen Alexandra Hospital, in Cosham.
She added: ‘The driver of the car was not injured.’