McCartney began his career at the Collingwood Football Club amid a huge reputation from his junior football days. He could play at either end of the ground as a key positionforward or backman. After McCartney left the Magpies after four seasons from 1991–1994, he switched to Adelaide, with whom he had a good debut season in 1995. He missed out most of the year due to the strength of the team in 1997, therefore missing the Crows' first premiership triumph. So he moved to North Melbourne, where he played in the 1998 losing Grand Final against the Crows. In 1999 he once again had the opportunity to play in a Grand Final, but was suspended during the preliminary final against Brisbane saying that it was the worst day of his life, and went on to miss the Roos' premiership triumph that year. He then played in the team that made a losing preliminary final in 2000, which was the last finals match he played, and could have been considered unlucky, considering circumstances, to have never played in a premiership. In 2002 he had a poor season after being forced to fill the key forward role vacated by champion Wayne Carey who did not compete in the 2002 season having left the club following a sex scandal with Anthony Stevens' wife.
Bali bombings
On 12 October 2002, McCartney was a victim of the Bali bombing near the Sari Club. He was drinking at a nearby pub called Paddy's Bar when the bomb exploded, causing McCartney and his companion, fellow AFL footballer Mick Martyn, to suffer the impact of the blast. Martyn escaped with minor burns, while McCartney suffered severe second degree burns to over 50% of his body. McCartney initially thought his burns were minor and set about saving those around him instead of worrying about himself. He considered others to be in more pain than he was, and had to be taken on a special chartered flight back to Melbourne along with other victims. When he arrived the injuries turned out to be severe and McCartney almost died during surgery. He was awarded a Medal of the Order of Australia for his support to other victims. What followed was a long rehabilitation process. McCartney stated that his objectives were to marry his fiancée Nerissa, as planned, and also to return to AFL football. The comeback was seen as an almost impossible task.
Return to AFL football
He married fiancée Nerissa Vanderheyden on 14 December, just 63 days after the bombings. Throughout 2003, McCartney rehabilitated with the intention of regaining his place in the Kangaroos on merit. Following an early season thigh strain, McCartney eventually played seven games with the Kangaroos' then-VFL affiliate Port Melbourne before gaining senior selection. On 6 June 2003, McCartney returned to the AFL. Playing for the Kangaroos against Richmond, McCartney was heavily bandaged, wore a long-sleeved top and had to wear protective gloves. McCartney wore the numbers "88" and "202" on his guernsey – 88 representing the number of Australians who died in the Bali bombing, and 202 the total number of deaths, with many in the crowd also holding up the numbers on signs. McCartney had the modest statistics of 3 kicks, 1 mark and 1 goal, 1 behind. He booted a goal early in the final quarter, but with the Kangaroos trailing by less than a goal late in the game, McCartney dished off the ball to Leigh Harding, who scored the winning goal with seconds remaining. In a real twist to the night, McCartney announced his retirement from AFL football during his on-field post-match interview, citing that his road back had left him spent and that he preferred to leave on a high note. To this day, it is considered one of the most inspirational sports-related stories in Australia, with Fox Footy's AFL: The Greatest ranking it as #7 on its list of the biggest AFL news stories of all-time. The image of McCartney being chaired off the groundafter the game is captured in Jamie Cooper's painting the Game That Made Australia, commissioned by the AFL in 2008 to celebrate the 150th anniversary of the sport.
Post-retirement
As of 2003, the Jason McCartney Medal has been awarded to the player judged most courageous on field in games between Collingwood and North Melbourne. Following his retirement, McCartney wrote After Bali, which recounted his ordeal. He is also a prominent motivational speaker on the public speaking circuit around Australia. He was an assistant coach at the Calder Cannons in the TAC Cup in 2009 and joined Fremantle as a development coach for the 2011 season. He then moved back to Melbourne to be the Western Bulldogs' list manager at the end of 2011. He left this role post the 2017 season and moved to Sydney to be the GWS Giants list manager.
