Mollie Grace O'Callaghan OAM (born 2 April 2004) is an Australian swimmer and the reigning Olympic champion in the 200 m 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.

O'Callaghan swam for the Australian team in the preliminaries of all three women's relays at the 2020 Summer Olympics in Tokyo, receiving two gold medals and one bronze for her contribution.

Swimming the 1st leg for Australia in the heats of the 4 × 100 metre freestyle relay, she posted a time of 53.08 and received a gold medal after the Australian team won the final.

[2] In the 4 × 200 metre freestyle relay preliminaries, O'Callaghan swam a junior world record of 1:55.11 when swimming the lead off leg.