The 19-year-old full-back has been training with North End since the summer after leaving the Magpies and has impressed boss Simon Grayson enough to earn a deal for the rest of the campaign.
"He is a young lad who we like the look of and hopefully he will develop into a good footballer and be part of the Preston squad for a long time to come," said Grayson.
"He is a right-back who can play further up the pitch as well, he has got a good pedigree in terms of his upbringing at Newcastle United.
"He is an attacking full-back, he trained with us a few times last year at the back end of the season and he has been with us all pre-season right the way through to now and obviously with one or two going out, it has released a little bit of funds for us to make sure Alex can come in on a full-time basis
"He never thought he was going to make it up there hence why he wanted to leave at the end of last season and we have liked what we saw last year when we watched him and since he has been with us."