The incident near junction 23 was first reported, at about 2pm, as a multi-vehicle collision by Traffic Scotland.
A Police Scotland spokesperson said: “Police responded to a concern for person call on the M8 motorway near to Junction 23 westbound.
“Emergency services attended and a 56-year-old man was pronounced dead at the scene. Next of kin have been made aware.
“The road was closed for around three hours and a report will be submitted to the Procurator Fiscal.”