Dr Thomas Munch-Petersen lost control of his car while searching for a mint in a jacket draped over his passenger seat.
Two men and a pregnant woman died in the pile-up caused by his car veering from the overtaking lane of the motorway.
The accident happened on the M1 in Derbyshire in April last year.
It hit a lorry, which then careered back across the road, taking the Volvo with it.
Both vehicles went through the central reservation and into the path of the oncoming traffic.
Darren Kempton, 32 and his pregnant girlfriend Jenny Lancaster, 25, from Milton Keynes, were killed when their car hit the lorry.
Research trip
Martin Parker, 44 of Harrogate, Yorkshire also died after his car hit the wreckage.
His wife and 15-year-old daughter escaped serious injury.
Derby Crown Court heard that Munch-Petersen, a university lecturer was travelling from London to Leeds to carry out research when the accident happened.
He told the court: "It was a grave misjudgement. I have no positive recollection of taking my eyes off the road, but I accept I must have done."
Sentence adjourned
Dr Munch-Petersen, of East Twickenham, Middlesex, had admitted careless driving but denied causing death by dangerous driving.
Sentence has been adjourned for reports.
Judge Granville Styler granted bail but said: "Three people have died. A custodial sentence is almost inevitable."