The Auto Cycle Union confirmed a second rider was killed in Thursday's Supersport TT Race 2 on the mountain circuit.
Forty-eight-year-old Austrian Martin Loicht died in a crash at Quarry Bends.
He was competing in the TT for the first time since the 1990s, and also had experience of racing on the Isle of Man at the Southern 100.
Martin Loicht was a professor of mechanical engineering at the Institute of Technology in Vienna.
He was married to Nikola and had two children.
The Auto Cycle Union passed on its deepest sympathies to the rider’s family and friends.
Technical director of the ACU Dr Paul King said: 'I got to know Martin really well by working with him on the TT Zero project as he was developing a bike to compete in that race.
'He was a real character who was passionate and committed to motorcycling and he reflected the amateur spirit and endeavour that pervades the TT.'
The other rider who lost his life in the Supersport TT Race 2 was Paul Dobbs from New Zealand, who crashed at Ballagarey.