Early years

McSweyn grew up on a beef and sheep farm on King Island (population 1600) in the middle of Bass Strait, south of Melbourne, Victoria.

There was no high school on the island, so he boarded at Ballarat in Victoria. Being away from home at a young age, he built resilience which helps him cope with being overseas for lengthy periods of time.^[3] Up until he was 14 years old he played cricket, tennis and AFL, but then decided to concentrate on athletics. At Ballarat he was coached by Rod Griffin, distance runner Collis Birmingham and his now training partner Brett Robinson.

McSweyn represented Australia at the 2013 World Cross Country Championships in the junior race and in 2015 he ran the 5000m at the World University Games.^[3]

International competition

Beginning in 2016, McSweyn started regularly competing on the international circuit.

He represented Australia in the 3000 metres steeplechase at the 2017 World Championships.

In 2018, McSweyn placed third in both the 5000m and 3000m steeplechase races at the Gold Coast Australian Championships in February. In April at the Commonwealth Games, McSweyn placed 5th in the 5000m final in 13:58.96 and 11th in the 10,000m final in 28:58.22 respectively.^[4] At the Shanghai Diamond League meet, McSweyn placed 11th in the 5000m. He raced the 10,000m race at the Oslo Bislett Games in June and the 1500m in Germany, followed by Rabat Diamond League, where he placed third in a competitive 3000m field in 7:34.79. The time put him within two and a half seconds of Craig Mottram's Australian record in the event. He then raced in the London Müller Anniversary Games 5000m, finishing 12th. In August, McSweyn raced a mile at the Birmingham Müller Grand Prix, winning in 3:54.60. He then competed in the Rovereto Palio Città della Quercia in Italy, clocking 13:31.03 for 5000m. Notably, at the Bruxelles Memorial van Damme Diamond League Final, McSweyn achieved a 13:05.23 personal best over 5000m, finishing 12th in the race. Back on home soil in 2018, McSweyn rounded out his 2018 season by winning his second straight Melbourne Zatopek:10. His 27:50.89 brought him his second straight Australian 10,000m title.^[4]

In December 2019, McSweyn broke the Australian record for 10,000m, running 27:23.80 at the Zatopek:10, his third successive national championship at the distance.^[5]

In July 2021, McSweyn broke the Australian record for the mile, running 3:48.37, beating the record set by Craig Mottram in 2005 by 0.61 seconds.^[6]

In August 2021, at the Tokyo Olympics, his time of 3:31.91 in the 1500 metres earned him seventh place.^[7]

In February 2023 at the World Athletics Cross Country Championships, held in Australia, McSweyn achieved a bronze medal in the mixed relay, alongside Oliver Hoare, Jessica Hull and Abbey Caldwell.^[8]