Thornton made his Twenty20 debut playing for the Sydney Sixers in the 2016–17 Big Bash League against the Brisbane Heat on 3 January 2017. He opened the bowling and bowled his full four overs with figures of 1/40.[3] Though it was the only BBL match he played for the season, he made his List A debut a week later playing for Cricket Australia XI in a tour match against Pakistan. He bowled 10 overs, including a maiden, and had figures of 3/69.[4] Later in the season Thornton played a Twenty20 tour match against Sri Lanka, this time playing for the invitational team Prime Minister's XI. He bowled 2.1 overs with figures of 0/24.[5]
Thornton was included in the Cricket Australia XI squad for the 2017–18 JLT One-Day Cup. He played three matches during the tournament, bowling at an economy rate of 5.64, but he was only able to take two wickets.[6]
Four years after his Big Bash debut, Thornton played his second match in the competition, appearing for Adelaide Strikers in a 2021–22 match against Brisbane Heat. He took one wicket for the cost of 12 runs in three overs, generating some "eye-catching late movement" during the match.[7]
In December 2022, Thornton took 5/3 to help bowl the Sydney Thunder out for 15, the lowest score in a professional T20 match.[8]