is an Australian professional football manager and former player who is currently the head coach of the Iraq national team. Arnold was first appointed to work as a head coach of the Australian national soccer team in 2000. After head coach Frank Farina was sacked in 2005, Arnold worked with Guus Hiddink for the 2006 FIFA World Cup campaign, in which they made the second round of the finals. After Hiddink left, he became interim coach of the Socceroos. Arnold went on to qualify Australia's U23 men's national soccer team (nicknamed the Olyroos) for the 2008 Beijing Olympics. Arnold then went on to assist Pim Verbeek for qualification of the 2010 World Cup in South Africa. Arnold's next move was to take the manager role at struggling A-League club the Central Coast Mariners between 2010 and 2013, where he guided the club to a Premiership and a Championship. He is a member of the Football Federation Australia Football Hall of Fame. Arnold went on to win two Premierships, one Championship and an FFA Cup with Sydney FC. In August 2018, Arnold was appointed head coach of the Socceroos - Australia's senior men's national soccer team.

In 2018, Arnold replaced Bert van Marwijk as Australian coach after the 2018 FIFA World Cup. Under Arnold, Australia qualified for the 2022 FIFA World Cup, during which Australia achieved their most successful World Cup campaign: after recording multiple group stage wins for the first time, with their only group stage loss being to eventual runners-up France, Australia qualified for the Round of 16 for the second time in their history, where they narrowly lost to eventual champions Argentina. He resigned from the role in September 2024.

Arnold holds a number of A-League records: he has managed the fourth most games of any manager in the A-League (211), he has achieved the third most wins in the competition's history (116), he has the third-best career winning percentage of any A-League manager with 30+ games managed (54.9%), he has the best career unbeaten percentage of any A-League manager (81.5%), and he is one of just three managers to have won multiple A-League championships. Arnold also holds the records for most games coached, and most games won, as manager of Australia.