The 27-year-old is understood to have signed a three-year deal, having agreed personal terms and passed a medical. No transfer fee is involved.
The Scottish Premier League's all-time record goalscorer, Boyd spent the second half of last season on loan with Nottingham Forest after joining Boro from Rangers in the summer on a Bosman transfer.
He scored six goals for Boro and a further six for Forest.
Source: Northern Echo
Source: Northern Echo