Ranocchia, 28, arrives from Inter Milan on loan until the end of the season, becoming Marco Silva's sixth arrival of the January window.
According to the Evening Standard, Tottenham and West Ham United were also assessing the possibility of signing the Italy international. After losing Jan Vertonghen to an ankle injury, reports suggested Mauricio Pochettino had been considering bringing in the experienced defender as cover, but Ranocchia will now spend the rest of the season at the KCOM Stadium.
He joins fellow new arrivals Markus Henriksen, Oumar Niasse, Evandro, Omar Elabdellaoui and Lazar Markovic to help Hull fight for Premier League survival.
Hull are yet to confirm whether their new defender has been registered in time to make his debut against Manchester United on Wednesday (30 January), but the Italian hopes to be involved at Old Trafford.
"I want to contribute to this team and this is a great opportunity for me to play in the Premier League," he told Hull's official website.
"It is a famous league throughout the world and I have watched the last three games that this team has played. The coach here is very good and we have some very good players.
"I am a tall defender so I am good in the air, but I am also happy with the ball at my feet. We have a big match against Manchester United on Wednesday night and if I can play I will be very happy.
"But there are a lot of matches left in the season and the longer objective is for the team to be safe. This is what I want to help with."