According to reports, the incident happened on the seafront, west of the roundabout by the Sealife Centre, at around 3am today (Sunday, April 17).
The road was closed to traffic while emergency services investigated.
It was reopened earlier this morning.
A spokesperson for Sussex Police said: “Police were called shortly after 3am on Sunday (April 17) to reports of a collision involving a blue BMW car and a pedestrian on the A259 Kings Road in Brighton.
“The pedestrian - a 28-year-old woman - was taken to the Royal Sussex County Hospital in a critical condition.
“Officers investigating the collision would like to hear from anyone who saw what happened, or who may have captured any relevant CCTV or dash cam footage from the area.
“Anyone with information is asked to contact police online or by calling 101 quoting Operation Autumn.”