As a player, he spent most of his club career as a defender for South Melbourne Hellas and played four games for the Australia national team in the late 1980s.

After his father, Dimitris ("Jim"), lost his business following the 1967 Greek military coup, the Postecoglou family migrated to Australia in 1970, when he was five years old.

[1][9] After first joining South Melbourne Hellas as a nine-year-old,[10] Postecoglou rose through the youth ranks to play 193 games from 1984 to 1993 for them in the National Soccer League as a one-club player.

[22] Postecoglou started rebuilding the team by releasing Liam Reddy, Craig Moore, Bob Malcolm and Charlie Miller.

Tommy Oar, Michael Zullo and Adam Sarota were bought by Dutch club Utrecht, and striker Sergio van Dijk went to Adelaide United.

[23] Postecoglou, who asked to be judged a year from the time he took over, proved the critics wrong by winning and playing an entertaining brand of football.

[28][29] Postecoglou led the Roar to the Premiership and Championship in the 2010–11 season, winning the Grand Final 4–2 on penalties against the Central Coast Mariners in front of 52,168 people at Lang Park.

[31][32] In the 2011–12 season, Brisbane Roar became the first team to win back-to-back A-League championships and Postecoglou became the most successful Australian domestic football coach, with four national titles.

Postecoglou left the Roar after two-and-a-half years, during which he led the club to back-to-back A-League championships, a premiership and consecutive qualification for the AFC Champions League.

[citation needed] Postecoglou was appointed head coach of the Australia national team on 23 October 2013 on a five-year contract, replacing German Holger Osieck.

[36][37] Postecoglou was tasked with regenerating the Australian national team, which was deemed to have been too reliant on members of their Golden Generation of 2006, subsequently leading to a stagnation of results that culminated in successive 6–0 defeats to Brazil and France.

[47][48] Postecoglou coached Australia in 2015 AFC Asian Cup, where they beat Kuwait (4–1) and Oman (4–0), but lost to South Korea (0–1) in the group stage.

[50] On 19 December 2017, Yokohama F. Marinos announced they had appointed Postecoglou as head coach with his tenure set to begin after the 2017 Japanese Emperor's Cup.

[55][56] After an initial difficult start to the season, which saw Yokohama F. Marinos facing potential relegation,[57] Postecoglou guided the club to the final of the J-League Cup, and a 12th-place finish in the league.

[63][64][65][66] Celtic, who had just lost their league title to Rangers for the first time in a decade, had abruptly missed out on hiring English manager Eddie Howe.

The new appointment was mocked by Celtic fan and Talksport presenter Alan Brazil, who apologised on his show a year later, after Postecoglou had won the league.

[21] Postecoglou's first game was a UEFA Champions League qualifier on 20 July, drawing 1–1 against Danish Superliga club FC Midtjylland;[68] a 2–1 loss in the second leg in Denmark led to elimination eight days later.

[71] The following 2 February, a 3–0 win over rivals Rangers put Celtic to the top of the league table for the first time in the season, ending a 13-game unbeaten start for opposing manager Giovanni van Bronckhorst.

[73] Though some sources called Postecoglou the first Australian to win a league title in Europe,[74] he was preceded by several weeks by Anthony Limbrick, who won the Cymru Premier for The New Saints.

[81] Celtic ended the season with a record eighth domestic treble after they won the Scottish Cup at Hampden Park against Inverness Caledonian Thistle on 2 June in Postecoglou's last match in charge.

[83] On 6 June 2023, it was announced Postecoglou will be appointed head coach of English club Tottenham Hotspur, starting 1 July, on a four-year contract.

[86] On 24 September, Postecoglou became the first Tottenham manager to earn points from Arsenal away at the Emirates Stadium in four years since Pochettino, after the North London derby ended in a 2–2 draw.