Billy, 34, has signed for Celtic on a permanent deal after being released from his contract at the Shay.

The ex-Huddersfield and Carlisle man was made available by Chris Wilder on the eve of the new season after being told he would not figure in his plans.

Billy, who also had spells with Plymouth, Bury and Notts County, made 13 appearances for Halifax last season after signing from Carlisle in January.