Born in Newport, South Wales,[1][2] Collier began refereeing on the professional snooker circuit in 1992.

[3] In 2004, he took charge of the World Snooker Championship final between Ronnie O'Sullivan and Graeme Dott where he also became the youngest referee to take charge of a world championship final.

[3] Eighteen months after the 2004 final, in 2005, Collier quit the main tour, citing the lack of financial rewards in his profession.

[4] He was persuaded by Barry Hearn to re-join the main professional tour in 2011, with the additional opportunity to work as a Tournament Director.

[4] In 2016, he refereed the final of the 2016 World Snooker Championship between Mark Selby and Ding Junhui.