Tallis Duncan (born 18 April 2002) is an Australian professional rugby league footballer who plays as a lock for the South Sydney Rabbitohs in the NRL.

[11][12] Duncan was named in the Malta international side and represented them on 22 June against the Lebanon national rugby league team.

[16][17] Duncan made his first grade debut from the bench in his side's 33–26 loss to the Canberra Raiders at Stadium Australia in round 13 of the 2023 NRL season.

[18] In round 19 of the 2023 NRL season, Duncan scored his first try in the top grade as South Sydney lost 36-32 against the Canterbury-Bankstown Bulldogs.

Duncan played 20 games for South Sydney in the 2024 NRL season as the club finished second last on the table after a difficult campaign.