The 20-year-old enjoyed a successful loan spell with the Tigers last season scoring five goals in 11 appearances and Hull boss Peter Taylor was keen to have him back at the club.
Hull have paid an initial fee of £50,000 for the former Blackburn ace, and Taylor was delighted to bring him in.
"He was perfect for us last season and, because he is only 20, is only going to improve," said Taylor.
"I know people are going to have a go at us for spending a few more bob for a Third Division side, but nine times out of 10, the players we have brought in are under 21.
"Jon is another one who is very much one for the future."
