Casserly made his senior debut for Marconi in the National Soccer League as a 17-year-old, and quickly established himself as an integral part of the first-team squad winning the National Soccer League championship in 1992/93.

An enterprising wing back, Casserly spent seven seasons with Marconi, earning International honours at Under 20 and Under 23 level, and ultimately making his full senior debut under Terry Venables against New Zealand in 1997.

He was lured to Northern Spirit in 1998, the newly formed National Soccer League franchise based in North Sydney.

However, he failed to negotiate an improved contract, and returned to Australia, playing out the final seasons of the now defunct NSL with Marconi.

[1][2] Despite the dawn of the A-League, Casserly elected to pursue more lucrative career interests outside of football, and continued to play football at the NSW Premier League level, where his clubs have included Marconi, Stanmore Hawks, Blacktown City and Manly United.