The collision between a Ford Ka and a Ford Focus happened on the A1 near Torness power station in Dunbar, East Lothian, at about 7.40pm on Thursday, January 9.
The Focus driver, 23-year-old David Forsyth from Invergordon, Highland, was taken to hospital after the collision but has since died, police said.
Dawn Morris, the 21-year-old driver of the Ford Ka, was pronounced dead at the scene. Her rear seat passenger, 21-year-old Claire Jamieson, died in hospital last week. Both women were from the Cowdenbeath area of Fife.
Two other 20-year-old women, who were passengers, were injured in the crash.
An investigation into the full circumstances surrounding the incident is continuing, Police Scotland said.