The TT returns in 2022 after a two-year absence as a result of the COVID-19 pandemic, with action beginning last Sunday with the first official qualifying sessions.
Running continued through Monday, Tuesday and Wednesday, with this evening's running consisting of a lap for Sidecars, followed by a Superbike, Superstock and Supersport session.
At just after 8pm local time, the session was red-flagged for an incident at the ultra-fast Ballagarey section of the 37.75-mile Mountain Course.
The following Sidecar session was cancelled as a result of the incident, with TT organisers announcing at around 10:30pm on Wednesday night that Welsh rider Purslow had died as a result of the accident.
Purslow was contesting his second TT having made his debut back in 2017, after wins on the course in the Manx Grand Prix.
A statement from TT organisers read: “The Isle of Man TT Races regrets to confirm that Mark Purslow, 29, from Llanon, Ceredigion was killed in an incident during the fourth qualifying session of the 2022 Isle of Man TT races.
“The accident occurred at Ballagarey, before the fourth mile marker, on his third lap of the session.
“Mark made his first appearance on the TT Mountain Course at the 2015 Manx Grand Prix where he won the Lightweight Race on his debut. He graduated to the Isle of Man TT Races in 2017, competing in the Supersport and Lightweight classes – 2022 was his second TT.
“Mark was also an experienced classic racer, competing at the Classic TT in 2016, 2018, and 2019, with a best result of 14th in the 2019 Junior Classic TT.
“Mark had set his fastest ever lap of the TT Mountain Course at 120.86 mph earlier in the session, his first lap in excess of 120 mph.
“The Isle of Man TT Races pass on their deepest sympathy to Mark’s family, friends, and loved ones.”
On Tuesday evening another rider, Dave Moffitt, was airlifted to hospital in Liverpool after an accident in the Lightweight class qualifying session.
He is said to be in a “serious but stable condition”.