In 1989, while playing for Cudgen, Mathiou represented the New South Wales under-17 team in their 16–8 win over Queensland under-17.[3] In 1990, he joined the Gold Coast Seagulls, playing for their lower grade sides.
In 1992, Mathiou joined the North Sydney Bears. In Round 18 of the 1992 NSWRL season, he made his first-grade debut in the Bears' 12–26 loss to the St George Dragons. Over two seasons with North Sydney, Mathiou played four games.
In 1995, he joined the newly established North Queensland Cowboys. He played seven games for the club in their first season. In 1996, he played just four games before departing the club at the end of the season.
In 1997, Mathiou joined the Leeds Rhinos, where he would go on to play 136 games for the club, starting 100 from the bench. He became the longest-serving import for the club since the change of import rules in 1982.[4] In 1998, he came off the bench in Leeds' 1998 Grand Final loss to the Wigan Warriors. In 1999, he came off the bench in Leeds' Challenge Cup win over the London Broncos.
After retiring, Mathiou spent time coaching the Cudgen Hornets and worked as a recruitment coordinator for the Sydney Roosters from 2005 to 2014.[7][8][9] In 2015, he joined the Gold Coast Titans as the recruitment manager, spending only a year at the club.[10] In 2016, he returned to the Roosters as a member of the recruitment team.
