Charnley made numerous appearances for the Under 20s in 2010 before joining Blackpool Panthers on dual registration and then Hull Kingston Rovers on loan. He was a player around the fringes of a first team opportunity at Wigan before the possibility came to join Hull Kingston Rovers for a month. Injuries meant he was given the chance to play first team rugby by Hull KR coach Justin Morgan, making his Super League debut. Charnley showed great promise on his debut for Hull KR against Leeds Rhinos and picked up the club man of the match award. He scored five tries in five appearances,[7] including a hat-trick in a home win over Castleford Tigers, and the opening try in the derby clash with Hull FC.
He played on the wing in the 2011 Challenge Cup Final victory over the Leeds side at Wembley Stadium. Charnley scored the first try, and broke a bone in his hand in his side's victory over Leeds.[8][9]
In the 2012 Super League season he scored 31 tries to help Wigan to the League Leaders' Shield. This put Charnley in third place in the all-time top try scorers in a regular season in the summer era as only Lesley Vainikolo (36 tries) and Danny McGuire (35 tries), both in 2004, have scored more tries in a Super League regular season.
Although the game ended in a 36–14 defeat for Wigan, Charnley scored two tries in the 2014 World Club Challenge against NRL champions the Sydney Roosters. On 18 June 2014, he scored five tries in a 48–4 victory over Widnes Vikings. Despite missing two months of action due to a knee injury, Charnley still scored at a rate of over a try a game with 23 tries in 21 games in the 2014 season.
On 30 March 2016, Charnley made the cross-code switch to rugby union with Manchester-based Sale Sharks, who compete in the Aviva Premiership, for the 2016–17 season.[22] Charnley was not able to repeat his scoring success in rugby union, bagging four tries in 32 games. Charnley then returned to rugby league for the 2018 summer season, his last game in rugby union coming against London Irish in February.
On 25 June 2022, Charnley signed an initial loan deal with Championship side Leigh with a permanent contract starting in 2023. On 10 July 2022, Charnley made his debut for Leigh, scoring a try during a 66–0 victory over Workington Town.[26]
On 28 August 2022, Charnley scored two tries for Leigh in a 42–4 victory over Widnes.[27]
In round 3 of the 2023 Super League season, Charnley scored two tries including the winner as Leigh earned their first win back in the top flight defeating Hull Kingston Rovers 30-25.[28]
In round 6, Charnley scored a hat-trick as Leigh defeated Hull F.C. 24-16.[29]
On 12 August 2023, Charnley played for Leigh in their 17-16 Challenge Cup final victory over Hull Kingston Rovers.[30]
Charnley played 26 games for Leigh in the 2023 Super League season and scored 27 tries as the club finished fifth on the table and qualified for the playoffs. He played in their elimination playoff loss against Hull Kington Rovers.[31]
In May 2024, he scored his 300th career try in a win against Salford Red Devils.[32]
Charnley played 25 games for Leigh in the 2024 Super League season which saw the club finish fifth on the table. He played in the clubs semi-final loss to Wigan.[33]
International
Charnley made his representative debut for the England Knights in a friendly against France in 2011, scoring two tries and kicking four goals from six kicks.[34] He went on to make another scoring appearance against Cumbria one week later.[35]