[2] Regini-Moran began gymnastics at age three,[3] then the family moved to the Europa Centre in Crayford where Giarnni trained with coach Pete Etherington.

[3] In 2013, Regini-Moran's international breakthrough began at the competition in Brasília, Brazil for the 2013 Gymnasiade, he won gold in floor exercise, bronze in parallel bars and with Team Britain winning the silver medal.

In July 2016, Regini-Moran suffered a serious leg injury, damaging multiple knee ligaments and his hamstring and fracturing his tibia, which left him out of contention for the 2016 Summer Olympics.

[3] In October 2019, he was selected for the British team for the World Championships in Stuttgart, Germany, alongside Dominick Cunningham, Joe Fraser, James Hall, and Max Whitlock.

[3] In May, Regini-Moran was selected to compete for Great Britain at the 2020 Summer Olympics in Tokyo, Japan, alongside Fraser, Hall, Whitlock, and Jake Jarman (alternate).

In the qualification round, despite not qualifying for any event finals, his highest finish was 12th on floor, barely missing out on an alternate spot due to a tiebreaker with Takeru Kitazono (both scoring 14.666).

[7] In 2022, Regini-Moran was part of the same England/Great Britain team roster that competed in three successive competitions, alongside Fraser, Hall, Jarman, and Courtney Tulloch.

[18] After qualifying for the floor exercise final in fourth place, Regini-Moran won the gold medal in front of the home crowd with a 14.533, defeating the world and Olympic individual all-around champion, Daiki Hashimoto of Japan, by a narrow score margin of only 0.033.