The 27-year old winger arrives at the KC Stadium on a deal that runs until the end of the season before he will sign for a seven-figure fee in the summer.
Boyd has had plenty of interest in recent times and even saw a January move to Nottingham Forest fall over because he failed an eye test but will now suit up for the Tigers who sit second on the Championship table.
"The chairman Darragh MacAnthony and I spoke at length and he informed me he had turned down five bids from Hull City and three other bids from three other Championship sides because it was not about the money,” said Boyd.
"He was desperate to keep me at the football club so that Peterborough United had a better chance of retaining their Championship status.
"However, I explained that the opportunity to join a club like Hull City at this stage of my career was too good to turn down.
"After a long and emotional telephone conversation, he and the manager, reluctantly agreed to let me go and try and fulfil my dream.
"My message to the supporters is simple. Thank you very much for all your support over the time I have been with Peterborough. You have been magnificent."