Isle of Man TT organisers said French sidecar passenger Olivier Lavorel had died of his injuries, bringing the death toll from this year's event to six.
Lavorel suffered serious injuries and his compatriot Cesar Chanal was killed in a crash on June 4.
“Everyone at the Isle of Man TT Races is deeply saddened to today learn of the passing of Olivier Lavorel ...,” they said in a statement on Tuesday.
Olivier had been airlifted to a hospital in Liverpool after the crash, before being transferred to another hospital in France in late June, organisers added.
British Supersport rider Mark Purslow, Northern Irish veteran Davy Morgan and British father and son sidecar riders Roger and Bradley Stockton were the other fatalities at this year's races.
The event has been run since 1907 and ranks among the most dangerous in motorsport.
