Paul Hart said: "He's quick and he's hungry and he's available,"
"I've know about him for quite a while and we've kept tabs on him. Mick McCarthy confirmed he was a good lad when he was on loan up at Sunderland.
"He played in the Premiership for Leeds last season."
After signing Johnson told the the Official Barnsley FC Website: "The opportunity arose to come here yesterday after the two clubs agreed a deal so I was more than happy to join. I am looking forward to it and cannot wait to get my opportunity in a Barnsley shirt.