The accident happened on the A830 Road to the Isles at the railway bridge at Craigag, about two miles east of Glenfinnan in Lochaber, just after 3pm on Sunday.
There was no other vehicle involved.
The man, who has not been named, was taken to Belford Hospital in Fort William where he later died.
The road was closed for more than five hours to allow investigations to be carried out, leaving motorists with a 100-mile diversion.