The 49-year-old was being kept on life support after sustaining injuries that medics said were “not survivable”.
Miguet, who was from Normandy, was a regular competitor at the Isle of Man TT and Ulster Grand Prix road races.
"He had been racing at Dundrod for a long time and was a big character who had become part of the fabric of the event," said Clerk of the Course Noel Johnston.
"I have known Fabrice, or Mig as he is known to many, for over 20 years, even before I became clerk of the course.
"We have been in constant contact with his team and family since Saturday, both directly and via local authorities, and I am extremely saddened to know that he has succumbed to his injuries.
"Our thoughts are with Fabrice's parents and the Optimark team, as well as his wider circle of family and friends as they come to terms with their loss."
Miguet - owner of a motorcycle business - was competing for the Kawasaki/Optrimark Road Racing team.