The 22-year-old quit Ibrox last summer to join Championship side Cowdenbeath and has now won a big move after a fine campaign in Scotland's second tier.
Injury blighted Hemmings' Light Blues career as he struggled to hold down a regular place in Ally McCoist's plans.
But he showed what he could do for the Blue Brazil last term as he netted 24 goals in 39 games to keep the Fife side in the Championship and earn a place in the division team of the year.
He has now quit Central Park to sign a one-year deal with the Tykes and the former Gers star is determined to shine in the final third once again.
Hemmings said: "On the back of a good season I think this is a very good move for me.
"I want to hit the ground running, do well and continue what I did last season and score goals.
"I scored a couple of hat-tricks last season so if I can replicate that I will be happy.
"It was great to be nominated for the Scottish Championship Player of the Year award with the other players that were in the running.
"I was happy just to be in the mix, but to win the award it was quite an achievement for a Cowdenbeath player."
After swapping the Scottish Championship for League One in England, Hemmings has a chance to show what he can do at a high level.
And Tykes boss Danny Wilson is delighted to have landed his man after a long pursuit.
He said: "We've had our eye on Kane for quite a while.
The first time I watched him was when he played for Rangers a few seasons ago at a time when the club was having a few problems.
"A lot of the young players at that time split up from the club and went their own way which was what Kane also did when he went to Cowdenbeath and made a name for himself in league football.
"I've always been aware of him. When he was at Tamworth he was very highly rated which is why Rangers took him."