The 25-year-old will provide valuable cover with Bath having both Welshman Gareth Delve and Englishman Adam Vander on the injury list, and could even fit in at second row in the potential World Cup absence of Danny Grewcock and Steve Borthwick.
New signing Gray was born in Zimbabwe and represented them at Schools and Under-21 level, before moving to Australia where he was a member of the Australian Under-21 set-up.
He is British-qualified, and continues the Queensland connection at Bath, with head coach John Connolly and assistant Michael Foley both having been heavily involved with the Queensland Reds Super 12 side.
Gray signs from the Brisbane Broncos Rugby League club, where he has been for the last year, playing at centre rather than in the pack.
His decision to leave the 13-man game was not an easy one, but with coach Wayne Bennett not being able to guarantee him a place in the first-team squad of 25, the player told the Brisbane Courier-Mail on his departure: "If I was 20 I would be staying.
"The Broncos are a hell of a club and I have made some great friends. That's what makes it sad to leave."
His new Director of Rugby, Jack Rowell, said after the announcement of his signing: "Scott is a highly-skilled, athletic back row forward who can cover both blindside and No.8.
"He joins the club with good credentials having spent two seasons with the ACT Brumbies before switching codes for a year with the Brisbane Broncos RL, for whom he played centre.
"Scott is a very exciting acquisition in the key area of the back five and we are all looking forward to his arrival and integrating him into what is already a very good team spirit within the side."
Gray himself said: "This is an excellent opportunity for me and one which I am really looking forward to.
"Bath Rugby has a great pedigree and there are some excellent players at the club and I just can't wait to take to meet up with the squad, take to the training paddock and challenge for a place in the side ahead of the new Zurich Premiership season."
Gray becomes the 15th off-season signing for Bath as they aim to turn round their fortunes following a dismal campaign last season.
That tally is expected to become 16 later this week with an announcement set to confirm that South African centre Robbie Fleck will be joining the club from Currie Cup side Western Province, having been left out of the Springbok reckoning for the World Cup.
By Mark Smith