Gardai said the man, in his early 50s, was found in a burnt-out dark coloured Opel Zafira on the M4, about 1km from Kinnegad.
The vehicle was discovered on the eastbound lane at about 4pm on Monday.
Gardai and fire crews responded to the call.
Detectives in Mullingar, Co Westmeath, have appealed to motorists who may have seen the car driving in an erratic manner on the motorway or who may have information in relation to the incident to contact them.
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