She was one of three teenage girls walking on the carriageway of the H3 Monks Way next to Linford Wood, in the direction of the V7 Saxon Street when they were hit by a black Mercedes car.
All three suffered serious injuries as a result of the crash which Thames Valley Police believe took place at around 5.29pm.
This morning (22/4) Police confirmed one of the girls had died with an update to its appeal following the accident on Twitter, which stated:
"Sadly, one of the injured pedestrians, a 15-year-old girl has since died.
“Our thoughts are with her family and they are being supported by officers.
“We are continuing to appeal to anyone with info or dash-cam footage to come forward.”
Two of the pedestrians were taken to Milton Keynes University hospital with serious injuries and one was taken to the John Radcliffe hospital in Oxford also with serious injuries. All three teenagers are from Milton Keynes.
Police say the driver of the black Mercedes E Class remained on scene and did not require hospital treatment.
The authorities confirmed all three of the injured girls are from Milton Keynes.
A man driving the Mercedes remained at the scene, he did not need emergency medical assistance.
Investigating officer, PC Christopher Ruvolo-Jones, based at Milton Keynes, said: “We would like to talk to anyone who may have witnessed this collision or seen the pedestrians prior to entering the H3 Monks Way dual carriageway.