The 22-year-old defender has penned a two-year deal for the Scottish Championship club after impressing during a recent loan spell.
Beadling previously spent 14 years with Sunderland, joining the Black Cats’ set-up when he was eight years old.
He had been on the fringes of the first-team at the Stadium of Light for several seasons, both in the Premier League and the Championship.
But under a succession of first-team managers, from Gus Poyet to Dick Advocaat, Sam Allardyce to David Moyes, Simon Grayson to the recently-departed Chris Coleman, he failed to make the breakthrough.
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