Police said a blue Audi Q7 came off the westbound road near to junction 31 in Renfrewshire, west of Glasgow, around 5:05am.
Emergency services attended but two men, both aged 27, and a third man aged 31, died at the scene.
Five other men were taken to hospital with serious, but non-life threatening injuries.
Police said a 35-year-old man has been arrested in connection with road traffic offences following the crash.
The westbound carriageway of the M8 remains closed while an investigation by police in Renfrewshire and Inverclyde takes place.
Inspector Darren Cook, of Police Scotland’s Road Policing Unit, said: “Our thoughts go out to the family and friends of those who have lost their lives as a result of this crash.
“Our enquiries are currently ongoing to establish the full circumstances surrounding the incident.”.