The 21-year-old has agreed a one-year deal with the Silkmen after leaving Premier League giants Manchester City earlier this summer.
O’Brien progressed through the academy at the Etihad Stadium and has featured regularly for the City development squad.
He spent the second half of last season on loan with Scottish Championship side St Mirren, making fifteen appearances to help the club survive in the second tier.
O’Brien has also been capped up to under-21 level with Wales also had a spell on loan with Hyde United earlier in his career but will now link up with John Askey’s side where he will compete with Shwan Jalal for a spot in the Silkmen starting XI.