Grix is an Ireland international, making his début in 2006 against Russia.[7] He was named as captain of the Ireland squad for the 2008 Rugby League World Cup, and was one of his countries better players in the tournament.[8]
He later relinquished the captaincy to Liam Finn, however, he continued to feature for Ireland and was named in their squad for the 2013 Rugby League World Cup.
He is the older brother of fellow professional rugby league footballer Simon Grix, and cousin of professional association (soccer) footballer Michael Collins.
Grix runs a strength and conditioning facility in Halifax.[10]