Mitchell was handed a one-year deal after impressing during two years as a youth team player.
The imposing goalkeeper picked up some valuable experience on loan at Tamworth in 2010.11 and then at Lewes in 2011.12.
Dominant in the air and an impressive shot-stopper, Mitchell demonstrated enough to be offered a new contract at the end of last season.
At the start of 2012.13, the goalkeeper picked up valuable game time on loan at Mansfield Town and fully prepared him for his Magpies' debut in the FA Cup with Budweiser meeting with Rotherham United.
Mitchell concluded the season back with Tamworth, where he returned on a one-month loan deal.