French sidecar driver Olivier Lavorel, 35, died at an early stage of the race at Ago's Leap track on Saturday.
The competition was stopped and not resumed.
Driver Cesar Chanel was taken by ambulance helicopter to a hospital in Liverpool with serious injuries.
On Wednesday, 29-year-old Briton Mark Purslow died in a qualifier in the motorcycle class.
After his tragic death, the organizer announced: "The TT races will continue - but always with Mark in mind".
Including deaths regarding the Manx Grand Prix and Classic TT (TT stands for Tourist Trophy), the course has included 262 deaths since the start in 1907.