The shot-stopper admitted that leaving Oakwell was the hardest decision of his life and insisted the move was not motivated by financial gain.
"I want the fans to know how hard this decision was," he told the club's website. "It was the hardest decision in football that I've ever had to make.
"There were times when I thought I'd be here forever and I really did want to break all the records and play longer than anyone else.
"That made it more emotional for me to leave. Leaving is huge and I want to thank all of the fans for being so good with me from the start."
Steele, who joined Barnsley from West Bromwich Albion in 2008, made 227 appearances for the Tykes.