He played for Leeds between 1995 and 2000. He made his England and Great Britain débuts in 1996. In the 1997 post-season, Morley was selected to play for Great Britain in all three matches of the Super League Test series against Australia. Morley played for Leeds as a in their 1998 Super League Grand Final loss to Wigan. He won the Challenge Cup with Leeds in 1999 when they defeated 52–16 at Wembley. He was offered a chance to play alongside his brother Chris Morley, who played for Wales, but chose to commit to England in the 2000 World Cup. In July 2000, Morley agreed to join Australian side Sydney Roosters in the National Rugby League at the end of the season, who were being coached by former Leeds boss Graham Murray.
Sydney
The 2000 NRL season was Morley's first at the Roosters. After taking twelve months to fully acclimatise, the tough forward became a central figure in the club's twelfth Premiership – their first in 27 years – playing as a in the 2002 NRL Grand Final, a 30–8 victory over the New Zealand Warriors at Telstra Stadium. Having won the 2002 NRL Premiership, the Roosters travelled to England to play the 2003 World Club Challenge against Super League champions, St. Helens. Morley played and scored a try in the Roosters' victory. Later that year Morley played in the for the Roosters in the 2003 NRL Grand Final which was lost to Penrith Panthers. Morley played for the Roosters as a in their 2004 NRL Grand Final loss to cross-Sydney rivals, the Bulldogs. Morley was then selected in the Great Britain team to compete in the end of season 2004 Rugby League Tri-Nations tournament. In the final against Australia he played as a in the Lions' 44–4 loss. In a round 20 match towards the end of his final season with the Roosters, Morley was sent off after attempting to knee Bulldogs player Corey Hughes in the face as the player attempted to play the ball. Afterwards he was suspended by the NRL Judiciary, and the Roosters released him from his contract. He returned to the UK before the season's end. Morley had helped the Roosters to a World Club Challenge title as well as two further Grand Final appearances before joining English club Warrington. He is one of only eight Englishmen to have played in NRL Grand Final-winning teams. Morley is the only player to win Great Britain caps whilst at the Roosters, although Phil Clarke had won England caps whilst at the club.
Bradford
In 2005 Morley became the first Englishman to have won Premierships in the NRL and Super League and the Rugby League Challenge Cup. In late 2005, although still contracted to Roosters; Morley joined Bradford Bulls towards the end of the season and helped them to claim the Super League championship against his old team Leeds. He played for the Bradford Bulls from the interchange bench in their 2005 Super League Grand Final victory against the Rhinos. His stay at Bradford was short as he joined Warrington the next season.
Warrington
Morley signed a 4-year deal with Warrington, beginning in 2006. He captained the Great Britain test side that faced France in 2007. He was also appointed captain of Warrington. It was while playing for Warrington that he made his 400th competitive senior appearance. Morley was named in the 24-man England squad for the 2008 Rugby League World Cup, and also played against Wales at the Keepmoat Stadium, Doncaster prior to England's departure. In Group A's first match against Papua New Guinea he played from the interchange bench in England's victory. Morley guided Warrington to Challenge Cup glory in 2009, beating Huddersfield in the final at Wembley. He was selected to play for England against France in the one-off test in 2010. Morley captained Warrington in the 2010 Challenge Cup Final victory over the Leeds Rhinos at Wembley Stadium. Morley was to lead England in the 2010 Four Nations but was ruled out after injuring himself in a warm up match against the New Zealand Māori rugby league team. Morley played for England in the 2011 Four Nations. England made the tournament's final and in the final, Morley made his 50th international appearance. He played in the 2012 Challenge Cup Final victory over the Leeds Rhinos at Wembley Stadium. He played in the 2012 Super League Grand Final defeat by the Leeds Rhinos at Old Trafford. Morley's autobiography, "Moz", was released on 12 November 2012 and reprinted twice in the run up to Christmas 2012. He played in the 2013 Super League Grand Final defeat by the Wigan Warriors at Old Trafford.
Salford
Morley signed a one-year deal for his hometown club Salford for the 2014 season, aiming to finish his career with his hometown club. The 36-year-old forward was appointed the Salford Red Devils' captain at the start of the 2014 season. On 10 September 2015, Adrian announced that he would retire from playing rugby league at the end of the 2015 season. On 14 October 2015, it was announced that Morley would play one more rugby league match. In his last match, he represented his début club, Leeds, in a one-off exhibition game against New Zealand.
