A Brisbane Brothers junior, Valentine played for the Wests Panthers in the Queensland Cup from 1996 to 1999.
In 1999, due to a partnership between the Panthers and North Queensland Cowboys, Valentine joined the NRL club.
[5] In Round of 17 of the 1999 season, he scored his first NRL try in the Cowboys' 32–18 win over the Sydney City Roosters.
[6] Despite joining the club as a centre, Valentine transitioned into the forwards at the Cowboys, starting at second-row and eventually moving to prop.
Valentine suffered a number of concussions during his career, playing just 10 games over the next seasons.