Despite having been linked with moves to Tottenham Hotspur and West Ham United, Italy international Ranocchia has joined Marco Silva's side on loan until the end of the 2016-17 season.
He becomes the club's latest January recruit as Silva, who was only appointed manager himself at the beginning of the month, aims to rescue the club from a perilous position and maintain their Premier League status.
He faces a stern task on Wednesday with United unbeaten in the Premier League since October, but the club have confirmed the manager will be able to call upon his latest acquisition despite the 28-year-old's late arrival.
Hull have been decimated by injuries in recent weeks, with Curtis Davies the latest to be struck down. The Tigers captain is now expected to be out for eight weeks with a hamstring issue suffered in the FA Cup fourth-round defeat to Championship side Fulham on Sunday. Silva hopes Ranocchia can come in immediately to fill the void left by his skipper.
"Andrea is a good signing for us and he plays in a position that we needed to add to," said Silva at a press conference on Tuesday.
"We are happy with Michael Dawson, Harry Maguire and Curtis Davies but in these last games they do a lot to help the team. With the injury to Curtis now, we needed to bring in one more player.
"It was important for us that Andrea wanted to come here. He has had a very good career up to now and he is a player who can help our team at this level. He has the quality to help improve our squad. He has played for a lot of years with Inter Milan and he is an international player for Italy. He is experienced also."
Hull and United have already faced each other twice this month having been paired in the EFL Cup semi-finals. United cruised to a 2-0 win in the first-leg at Old Trafford but were given a major scare at the KCOM Stadium, losing 2-1 on the night but progressing on aggregate thanks to Paul Pogba's strike.