Speaking of his departure from Town, Davis told the Official Club Website: "I had a fantastic time at Ipswich and the only thing missing was promotion. The fans were terrific to me in my two years at the Club and I made many new friends there.
"The memories of my days at Ipswich will always be good ones and I wish the Club every success in the future. Hopefully they will make it to the Premiership next year, I'll certainly be cheering them on.
"But I think everyone gains from my move to Sunderland. Ipswich have got a fee that they can now invest in the squad and I've got a move to a Premiership club.
"Sunderland are a massive club with terrific support. Joining them appealed to me straightaway and obviously everyone wants to be playing at the top level and I'm no different."
Davis is the fourth player to leave Town this Summer. Darren Bent joined Charlton for a deal worth up to £3M earlier this month, whilst Drissa Diallo and Pablo Counago were released.
Tommy Miller, Shefki Kuqi, Fabian Wilnis and Jim Magilton meanwhile are currentley considering new deals at the club, with Wilnis having already indicating he will stay at Portman Road.