The youngster was out-of-contract at The City of Manchester Stadium and has decided to move to the North East with The Black Cats after signing a three-year deal with his new club.
A regular in the Citizens' reserves, the 20-year-old was Republic of Ireland Under-20's top goalscorer at the recent World Youth Championships in the United Arab Emirates.
Following the signing of his Sunderland contract, Elliott told the club's official website of his delight at moving to Wearside.
"With my contract about to expire at Manchester City, I had various options presented to me, but when I heard about Sunderland's interest I was thrilled," said Elliott.
"The prospect of joining Sunderland is very exciting and I am looking forward to having the opportunity to work with Mick McCarthy.
"Sunderland are a very ambitious club and although I know it's a cliche, they are a massive club.
"They deserve to be in the Premier League and, hopefully I can play a part in achieving this."
With Elliott arriving at The Stadium of Light, Sunderland have also been linked with fresh move for former Black Cats midfielder Don Hutchison, who is currently at Division One rivals West Ham United.
Meanwhile, Sunderland have signed youngster Richie Ryan on a new one-year contract at the club.
The 19-year-old's current deal was to expire at the end of the month, but he has extended his deal until June 2005.
