The Scotland international has signed a three-year deal with the Tigers.
Kingsley made just 19 appearances since moving to the Welsh club in 2014.
He told Hull's official website: "I'm delighted to get the deal done.
"It's come around quite quickly but I'm just delighted it's got over the line now and I can't wait to get training in the morning."
"It's time for me to really kick on now and get plenty of games at a very competitive level like the Championship."