The 22-year-old came off his Kawasaki machine in the Supersport race at the Crossakiel circuit, resulting in a red flag stoppage.
His family confirmed the tragic news on social media, with his brother Robbie saying he died 'doing what he loved'.
A statement issued to the News Letter by the Gardaí (Irish police) on Sunday evening said the young rider was pronounced dead at the scene.
“Gardaí and emergency services have attended the scene of a single vehicle collision at a closed racing circuit in Crossakiel Co. Meath, this afternoon, Sunday, 17th June 2022,” read the statement.
“The collision occurred at approximately 1:30pm and involved a motorcyclist.
“The motorcyclist, a man aged in his early 20s, was pronounced dead at the scene. His body has been removed to Navan Hospital.”
Jack had earlier finished as the runner-up in the Junior Support race and 10th in the Senior Support event.
The young Northern Ireland rider was a rising prospect in the sport and claimed his first Irish road racing victory at the Cookstown 100 in April, where he won the Senior Support race.
The tragedy comes after Co Down’s Davy Morgan was killed in a crash in the first Supersport race at the Isle of Man TT.
A highly experienced road racer, the 52-year-old was competing in his 80th TT race when the accident happened on the third lap at the 27th Milestone.
Davy arrived home from the Isle of Man on Sunday into Belfast and was escorted by to his home town of Saintfield by a large number of bikers, completing a lap of the now defunct Temple 100 road racing course.
His funeral will be held on Tuesday at Saintfield Presbyterian Church at a time still to be confirmed.