Demetriou returned to Australia in 2013, becoming the head coach for the
Northern Pride in the
Queensland Cup. During his two seasons at the Pride, the club won back-to-back minor premierships, the 2014 Queensland Cup Grand Final and the inaugural
NRL State Championship game. In 2014, he coached the Queensland Residents side, who defeated the
NSW Cup rep side 24–16.
In October 2014, Demetriou joined the
North Queensland Cowboys as an assistant coach.
[9]On 4 October 2015, Demetriou was a member of the North Queensland coaching staff in the side's 17–16
Grand Final victory over
Brisbane.
In January 2016, Demetriou joined the
St. George Illawarra Dragons as an assistant coach and as head coach to their
NSW Cupfeeder team, the
Illawarra Cutters.
[10] In September 2016, he was named coach of the 2016
Intrust Super Premiership NSW Team of the Year.
[11] He went on to win the grand final with the Cutters that year.
In 2017, Demetriou joined
Brisbane under head coach
Wayne Bennett.
[12] He took over as the side's attacking coach in Round 6 of the
2018 NRL season, with the side scoring the second most tries in the competition from that point forward.
[13]
In December 2018, he joined
South Sydney as an assistant coach, following Bennett to the club.
[14] In February 2020, it was announced that Demetriou would succeed Bennett as head coach at the end of the 2021 NRL season.
[15] On 6 August 2020, it was announced Demetriou would make his coaching debut for the
South Sydney Rabbitohs after head coach Wayne Bennett breached the NRL's COVID-19 protocols.
[16]His first match as coach saw the South Sydney club defeat
Brisbane by 28–10 at
ANZ Stadiumin Sydney.
[17]
Following the conclusion of the
2021 NRL season, he replaced the outgoing Bennett as the new head coach of South Sydney. In his first official game in charge, South Sydney were defeated 11-4 by
Brisbane at
Suncorp Stadium. In round 3 of the
2022 NRL season, he earned his first win in charge of South Sydney against arch rivals the
Sydney Roosters.
[18] In his first full season at South Sydney, he guided the club to their fifth straight preliminary final. Souths took an early 12-0 lead over
Penrith but were eventually defeated 32-12.
[19] In his second season at the club, Demetriou guided Souths to second place on the table during the midway point of the
2023 NRL season. However, the club would suffer a form slump in the second half of the year only winning four matches. South Sydney would finish 9th on the table missing the finals for the first time since 2017.
[20]
At the start of the
2024 NRL season under Demetriou, South Sydney lost their opening three matches of the season including a humiliating 48-6 loss against arch-rivals the Sydney Roosters. It was South Sydney's worst start to a season since 2008.
[21] Ahead of the clubs round 6 game against Cronulla, it was reported that Demetriou would be sacked as South Sydney head coach if they failed to win the match. Despite the team losing the match 34-22, Demetriou was not terminated due to an observable improvement in the team's effort for the game. The team would ultimately suffer yet another defeat after their subsequent bye, losing to
Melbourne 54-20. Although no formal announcement was made by the club about Demetriou's status immediately following the loss, it was reported that club officials would be holding an official meeting regarding his future.
[22] On 30 April 2024, the club formally terminated Demetriou as coach, appointing
Ben Hornby as an interim for the remainder of the season.
[23]
