Alasdair Macdonald, 78, was a passenger in a silver Suzuki Grand Vitara which crashed on the A857 at Newmarket, two miles from Stornoway, on Lewis.
The incident happened at around 10.20pm on Wednesday July 28.
He was taken to Western Isles Hospital and then transferred to the Queen Elizabeth University Hospital in Glasgow.
Police Scotland confirmed on Wednesday morning that Mr Macdonald, described as a local man, has died.
The driver, a 52-year-old woman, was also taken to Western Isles Hospital but was later discharged.