Kelly agreed a two-year deal, with the option of a further year, in the summer of 2011.
The attack-minded full-back, who can also play on the wings, arrived from Reading as one to watch for the future.
Living up to the references, Kelly went on to impress in his first season at Meadow Lane, making a total of 37 appearances across all competitions.
Mainly utilised at right-back, the former Arsenal trainee is always eager to join attacks and scored three goals in 2011.12, including a stunning volley against Tranmere Rovers.