The two-year deal, with an option for a third, could net the club in excess of £1m and will see the Cash Converters logo emblazoned on the club's new Adidas shirts.
"There was a lot of competition for a deal like this and it amounts to one of the biggest partnerships in the Championship," Hull City's chief executive Mark Maguire said.
"Cash Converters saw us as a very proactive club which is going forward and can help us develop their brand.
"They saw the huge potential here, and were impressed that we reach 250,000 kids each year through our community projects.
"They have also seen the investment into the club made by the Allams, the progress made on the pitch last season and our commitment to continually taking the club forward."
David Patrick, Cash Converters' chief executive, said: "We are very excited about the prospect of sponsoring the club as it looks to regain its place in the top flight.
"We looked at a number of clubs in the Championship and Premier League, but the stadium, fans new ownership and manager made Hull City the most appealing option."