Malachi Mitchell Thomas, 20, from Chorley in Lancashire, crashed his bike during the Supertwins race. He was riding for the Cookstown BE Racing team.
Mr Thomas was treated by medical staff at the scene but died from his injuries.
The accident happened on the course at Dhu Varren, Portrush.
The organisers of the event, the Coleraine and District Motor Club, offered their heartfelt condolences to the rider's family and team.
Racing at the event was cancelled following the fatal crash on Saturday.
Mr Thomas is a former Supermoto competitor and won a hat-trick of races at the Mid Antrim 150 in April.
He secured four podium finishes at the Tandragee 100 and won the Supertwins race at the Cookstown 100.
The English rider had earlier finished fourth in Saturday's Supersport race at the North West 200.
His death comes just a few weeks after another Manx Grand Prix winner, Billy Redmayne, lost his life at the Scarborough Spring Cup meeting.
An English rider has died following a crash at the North West 200 motorcycle races.