The 28-year-old completed a medical on Tuesday morning after the newly promoted club agreed a deal with the Championship outfit.
|11/10||Hull are 11/10 with Paddy Power to avoid relegation next season
"I'm delighted to be here," Davies told the club's official website.
"I feel that I'm joining Hull City at an exciting time and the chance to play in the Premier League was also a huge attraction. It's something that I've been lucky enough to do before and I wanted to get back to that level.
"Hopefully I can help this team to have a good season and push as high up the table as possible. I can't wait for Chelsea on the first day of the season now."
Davies has previous top-flight experience with West Brom and Aston Villa, prompting a call-up to Fabio Capello's first squad in February 2007, but is yet to make his senior bow.
The two-time England Under-21 international becomes Hull's second defensive signing of the summer following Maynor Figueroa's arrival from Wigan.