In early 2006, Ryan was involved in a tug of war between SL club Castleford Tigers and NRL club Wests Tigers, with both clubs claiming to have agreed terms with McGoldrick. In the end, he arrived in Castleford a few days before their first match of the season. Ryan McGoldrick made his début for Castleford Tigers in 18-42 defeat by Hull on 10 February 2006. He, along with the rest of the squad, battled to keep Castleford in the top flight. Ryan suffered a hamstring injury towards the end of the 2006 season, but was forced to play due to lack of numbers. Unfortunately Castleford were relegated at the end of the season. Despite this, McGoldrick signed a 2-year contract to stay with the club until 2008. McGoldrick played for the Tigers during the 2007 season, and was initially used in his less-preferred position of stand-off, which seemed to unsettle him. However, as the season progressed, he managed to move into the centre role and began to show fantastic form as Castleford won promotion back to Super League.