Mollie Grace O'Callaghan OAM (born 2 April 2004) is an Australian swimmer and the reigning Olympic champion in the 200 m freestyle. She was the 2023 world champion in the women's 100m and 200m freestyle individual events, and part of the world champion 4 × 100 m and 4 × 200 m Australian women's relay teams together with 4 × 100 m mixed relay team. She previously held the world record in the women's individual 200m freestyle.
O'Callaghan also won two gold and one bronze medals at the 2020 Summer Olympics as a heats swimmer in relay events and gold medal in the 200 m freestyle and 4 × 100 metre freestyle relay at the 2024 Summer Olympics.