[7] At the 2016 Junior Pan Pacific Swimming Championships, held in August in Hawaii, United States, Titmus won a silver medal in the 4 × 200 metre freestyle relay, splitting a 2:00.13 for the lead-off leg of the relay to contribute to the final time of 8:05.43, and a bronze medal in the 400 metre freestyle with a time of 4:09.81, which was 2.29 seconds behind gold medallist Li Bingjie of China.

[11] In the 4 × 200 metre freestyle relay the Australian team broke the world record setting a time of 7:41.50 with Titmus swimming the first leg.

[12] In 2019, Titmus was a member of the inaugural International Swimming League, representing the Cali Condors, who finished in third place in the final match in Las Vegas, Nevada, in December.

[14][15] Posting a new Olympic Record of 1:53.50 in the 200-metre freestyle final, she trailed behind Hong Kong's Siobhán Haughey for most of the race then came home strongly to push herself in front on the last lap.

[23][24] At the Paris 2024 Olympics, Titmus won Gold in the Women's 400 metres freestyle, finishing ahead of Canadian Summer McIntosh and American Katie Ledecky.