McGinty, 19, initially joined Carlisle at the beginning of November but is yet to feature for the Cumbrians.
The centre-half spent his formative years with Charlton before making the switch to Old Trafford in 2009.
Manager Greg Abbott told the club's official website: "He has come in and had a taste of the first-team atmosphere and he is improving all the time.
"This type of loan means that he can play development and reserve games for Manchester United but he's available for us if he's needed.
"He's a good lad and a hard worker and we think his time with us will have done him good."