The forward joins the Tigers for no fee after his previous deal at Blackpool expired.
The Tangerines will receive some money from the Premier League side, though, as Ince's age (22) means that they are due some compensation.
A statement on Hull's website read: "Negotiations between the Tigers and Ince's former club Blackpool over a compensation fee continue.
"Should the two clubs fail to come to an agreement, the fee will be determined by a tribunal."
Ince was close to moving to Italy, flying out for talks with Inter Milan that ultimately proved unsuccessful.