The highly-rated attacker brings a wealth of experience from higher up the football pyramid, having represented Southport, FC United of Manchester, Telford United and Warrington Town.
McCarthy originally joined the Purps in November 2020 following a serious knee injury and has since gone through his rehabilitation to return to full fitness.
Connor has impressed as a trialist during pre-season, bagging a number of goals and demonstrating his undoubted ability to supporters.
Purps boss Michael Ellison said: “Connor is a player we know really well, having worked together before at Runcorn.
“He’s a top lad on and off the pitch and I think everyone knows what he’ll bring to the side. He’s got that quality, he’s got that tenacity and he’s got goals in him.
“Connor has missed football for a long time with a knee injury which has been really unlucky, but what he’s done through pre-season is prove that he’s back to himself.
“He looks fit and strong, and he’s really got the bit between his teeth so hopefully he can make a real impact for us this season!”
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