Nanyn, 28, was named in the Championship Team of the Year after notching 20 tries and 102 goals this season.
Boss Ian Millward said: “We thought Mick’s form improved in the year but most importantly he wanted to stay at the club. The second thing was his scoring prowess – that’s pretty high.”
Nanyn joined Leigh in 2009 after failing to make an impression in Super League with Harlequins.
He has previously smashed club records at Oldham, Widnes, Whitehaven and Rochdale in the lower leagues.