Gavin Lupton, 37, was critically hurt at the Ulster Grand Prix on August 10, and has now died from his injuries.
He was racing in the Dundrod 15 Challenge at the County Antrim circuit when he crashed.
Another biker, Jamie Hodson, was also killed in a crash on the same day at the event.
The Dundrod and District Motorcycle Club, which organises the Ulster Grand Prix, described Lupton as an "experienced and popular rider".
"The Dundrod and District Motorcycle Club would like to offer its heartfelt condolences to Gavin's family, friends and team, and requests that their privacy is respected as they come to terms with his passing," the club said in a statement.