Mack Horton was born on 25 April 1996 and attended Caulfield Grammar from 2000 (Kindergarten at Malvern Campus) to 2014 (Year 12 at Caulfield Campus). He was Co-Captain of Malvern Campus in 2008 and in his final year at Caulfield was Co-Captain of boys’ swimming team that won the APS premiership. He was awarded triple colours for swimming and received the Caulfield Grammarians’ Swimming Club Prize for boys at the 2014 Speech Night.
Mack first represented Australia at the 2012 Junior Pan Pacific Swimming Championships in Honolulu, where he won gold in the 1500 metre freestyle in a championship record time. At the same meet, he finished second in the 400-metre freestyle and fourth in the 800-metre freestyle.
Mack won five gold medals and a silver medal at the 2013 World Junior Championships in Dubai and then qualified for his first senior Australian team by winning the 1500 metres at the 2014 Australian Swimming Championships and finishing second in the 400 metres, setting two junior world records in the process.
At the 2014 Commonwealth Games in Glasgow, Mack won the silver medal in the 1500 metres in a new junior world record time and narrowly missed the podium in the 400-metre freestyle, finishing in fourth place. He also swam in a heat of the 4 — 200-metre freestyle relay but was replaced in the team for the final, Australia going on to win the gold medal in a new games record time.
Three weeks later at the Pan Pacific Championships on the Gold Coast, Mack won the silver medal in the 800-metre freestyle, the bronze medal in the 1500 metre freestyle and was a member of the bronze-medal-winning 4 — 200-metre freestyle relay team. Mack then represented Australia at the 2015 World Swimming Championships in Kazan (Russia), where he won a bronze medal in the 800 metres freestyle.
In 2016 he became the first Victorian male swimmer and the first Caulfield Grammarian ever to win a gold medal at the Olympics when he took out the 400 metres freestyle on the first night of the swimming program in Rio de Janeiro. Mack also swam in both the heat and final of the 4 x 200 metres freestyle relay, in which Australia finished in fourth position, and placed fifth in the 1500 metres final.
At the 2017 Australian Nationals, Mack became the first swimmer to win the 200, 400 and 1500 metres freestyle events since Grant Hackett in 2008. At the 2017 World Championships in Budapest, Hungary, he was placed second in the 400 metres and third in the 1500 metres.
Mack was selected in his second Commonwealth Games team in 2018 and at the recent Games on the Gold Coast, he won the 400 metres freestyle, was second in the 200 metres and third in the 1500 metres. He was also a member of the winning 4 x 200-metre relay team.