The 24-year-old has signed a three-year deal, with an additional one-year option held by the Club, and adds to Nigel Adkins’ goalkeeping options.
Long has played under Adkins before during his time with the Blades and is delighted to be joining up with the Head Coach once again.
“I’ve known about the interest for a few weeks, so I’m excited to be here as a Hull City player now,” said Long.
“I’ve played under the Head Coach before and I really enjoyed that spell, so that was a big factor in me coming here. Hopefully I can continue to kick-on under him here.”
As well as having played more than 120 times for Sheffield United, his hometown club, Long has also had loan spells with Oxford United, Motherwell and, most recently, AFC Wimbledon where he impressed during 49 appearances for the League One side last season.