Parramatta Eels

Cayless started his career in the National Rugby League with the Parramatta Eels alongside his older brother, Nathan Cayless, who had already been with the club for three years.

In 2001 he made his representative début for New South Wales Country Origin.

Sydney Roosters

The following year Cayless moved to the Sydney Roosters and played for them at prop forward in their 2002 NRL Grand Final win over the New Zealand Warriors.

Having won the 2002 NRL Premiership, the Roosters traveled to England to play the 2003 World Club Challenge against Super League champions, St Helens. Cayless played at prop forward in Sydney's victory.

He played at prop for the Sydney Roosters in the 2003 NRL grand final which was lost to the Penrith Panthers.

Cayless played for the Roosters at prop forward in their 2004 NRL grand final loss to cross-Sydney rivals, the Bulldogs.

St Helens

Cayless played for St Helens as a prop forward in their 2006 Challenge Cup Final victory against the Huddersfield Giants.

St Helens reached the 2006 Super League Grand final to be contested against Hull F.C. and Cayless played as a prop forward in Saints' 26–4 victory.

As 2006 Super League champions, St Helens faced 2006 NRL Premiers the Brisbane Broncos in the 2007 World Club Challenge. Cayless played at prop forward in the Saints' 18–14 victory.

Wests Tigers

After spending four seasons in the Super League, in October 2009 Cayless signed with the Wests Tigers on a two-year contract starting in 2010.^[5] He started the first three games of the season from the bench, but injuries saw him make no further appearances for the Tigers in 2010. He announced his retirement before the start of the 2011 season.