Tangerine for Tierney
The 23-year-old becomes Simon Grayson's second signing of the summer after Rhys Evans signed from Swindon on a free.
Tierney who used to play for the Republic of Ireland's Under 21s plays at left back and it is hoped that he will solve the left back crisis at the club.
Tierney started his career at Manchester United but he only made one League Cup appearance for thr reds. In his time at United he went on loan, to Crewe, Colchester and Bradford City. He signed for Livingston last summer and went on to make 25 starts for the Scottish side last season.
He has initially signed a two year deal at Bloomfield Road with a view to a third year