The 22-year-old Liverpudlian, a popular figure among the Bucks faithful, scored 2 goals in twenty appearances last season.
He also had a one-month loan spell at Evo-Stik Premier side Warrington Town in the second half of the campaign.
He began his career Prescot Cables before moves to Skelmersdale United and Southport.
After shining in two loan spells from Southport, McCarthy was snapped up by Telford on a permanent basis in September 2016 but, despite a fantastic work rate and commitment to the cause, did not cement his place in the side.