He also coached at Wolves before returning to Southampton where he eventually became manager in 2001. On leaving the job, after a difficult time, he coached at both Villa and Wolves, acting as caretaker boss at both clubs, before becoming Northampton boss in 2007.
He left Sixfields earlier this season and now returns to the game with the Clarets.
Scouser Mercer, now 40, started out with Liverpool but didn't make the first team. He played over 100 games for Rotherham and almost 150 for Chesterfield whilst also playing for Sheffield United, Chesterfield and Bristol City.
He became goalkeeper coach at Bristol City but was recruited by Sheffield Wednesday in 2004 by then manager Chris Turner (himself a goalkeeper) and has been at Hillsborough since.
He's opted for a move to Turf Moor following the change of management at both clubs and he and Gray join Laws, Russ Wilcox and Graham Alexander in Burnley's new backroom team.
Also arriving at Turf Moor from Hillsborough are Tim Henderson (chief scout) and Dr Tom Little (fitness coach).