The incident happened on an unclassified road near Kilbryde Castle just outside the town, police said.
The 60-year-old man died at the scene at around 4pm on Saturday.
No-one else is thought to have been involved.
Meanwhile, a 24-year-old man seriously injured when his car struck a wall on Lewis on Saturday morning has been named locally as Iain Ruairidh Gillies.
Mr Gillies, who lives with his girlfriend in Skigersta, Ness, is the son of the district school's former headmaster.
He is fighting for his life in hospital in Glasgow after his Ford Focus smashed into a stone wall in the north of the island.
It happened shortly before 1am.
The force of the impact destroyed the front of the car.
No other vehicle was involved and he was the only person inside the car.
Mr Gillies was airlifted from Stornoway to the Royal Alexandra Hospital in Paisley for treatment.