[1] He made his List A debut for South Australia against Queensland on 28 November 2021 during the 2021–22 Marsh One-Day Cup.
[6] He is the identical twin brother of fellow cricketer Corey Kelly, who was born two minutes earlier; they have a younger sister, Lucy.
[5][7] Kelly spent his early career as a player for the Sturt Cricket Club, which he described in 2021 as being "in an awesome spot at the moment".
[8] At the age of 20, the Kelly brothers were signed to the West End Redbacks, South Australia's professional first class cricket team.
[8] Corey and Thomas Kelly are the first identical twins to play first class cricket on the same team in Australia since Kate and Alex Blackwell.