Nicholls signed a professional contract with the club in 2010 having completed his time as a scholar and working his way through to the Under 21 squad.
Along the way between 2010 and 2011 he was given experience of life at other clubs as he had brief loan spells with Hartlepool United, Shrewsbury Town and Sheffield Wednesday.
The giant stopper from Liverpool made his professional debut in February 2012 during a loan spell at Accrington Stanley at the end of the 2011/12 season, he made nine appearances in total.
In 2012/13 Nicholls enjoyed his best season to date as he moved to League Two promotion chasers Northampton Town on a season-long loan.
He made his mark straight away with a clean sheet on his debut away against Rochdale.
Nicholls played every single league game of the campaign, keeping 16 clean sheets in the regular season before playing in the playoff semi-final and final.
The Cobblers lost in the final to Bradford City but Nicholls set the semis alight with a clean sheet in both games and a Man of the Match performance in the second leg as he saved a penalty and Northampton beat Cheltenham 1-0.
Nicholls is capped internationally at Under 19 level and was involved in England's squad in the 2011 FIFA Under 20 World Cup but did not feature.