Lee attended St John Rigby College in Orrell from 2005 to 2007 and gained A-levels in subjects such as Physical Education and Business Studies.

In July 2009 it was announced that Lee would rejoin Wigan from his loan spell at Huddersfield due to injuries to captain Sean O'Loughlin and Harrison Hansen[8] He went on to make 11 appearances that season, scoring 1 try.

However, on 29 March 2010 Mossop signed a five-year deal at the Wigan club which would see him stay as a Cherry and White until the end of the 2014 season.

Mossop played in Wigan's 2011 Challenge Cup Final victory over the Leeds Rhinos at Wembley Stadium.

Mossop still came back on at half time despite his dislocated shoulder and played a pivotal role in the scoring of Jeff Lima's second try.

On 23 April 2013 Wigan Warriors and Parramatta Eels announced that Mossop would be joining the NRL competition for two years commencing 2014.

During this second spell at Wigan he played in the 2015 Super League Grand Final defeat by the Leeds Rhinos at Old Trafford.

[22] In round 11 of the 2021 Super League season, Mossop was sent off in Salford's match against Leeds after punching Konrad Hurrell.

In the announcement Mossop said "... after seeing the surgeon last week, he has told me there are no more surgeries he can offer to help prolong my career anymore and instead, it will be one final operation to give me a better quality of life with my wife and young children".