An Australia international and New South Wales State of Origin representative back, he captained the St George Illawarra Dragons of the National Rugby League from 2009 until his retirement in 2012.

Hornby played his entire career with the Dragons, leading them to the 2010 NRL Premiership and becoming their most capped player since the formation of the joint venture club in 1999.

The following season, Hornby played 27 games for St. George Illawarra as they once again reached another preliminary final with the opponent this time being Melbourne.

[5] On 3 October 2010, Hornby captained St. George Illawarra to their first Premiership in 31 years, when they defeated the Sydney Roosters 32–8 in the 2010 NRL Grand Final.

He represented New South Wales in the State of Origin series of 2004, 2006 and 2008 and played one match for Australia, their loss to Great Britain during the 2006 Rugby League Tri-Nations.