Trevor Sinclair has completed his £2.5m move from West Ham to Manchester City.
Sinclair passed a medical on Monday after agreeing to a four-year deal.
The England winger will now join manager Kevin Keegan's squad on their pre-season tour to Denmark.
City manager Kevin Keegan said: "In Trevor Sinclair we will have an England international at the peak of his career.
"He can play left side wide, right side wide and up front, so he will strengthen us and give us options."
Sinclair was born in south London but brought up in Manchester and supported City as a boy.
Middlesbrough boss Steve McClaren had initially tabled a £2m bid, then offered a player-plus-cash deal for 30-year-old Sinclair.
But Keegan has won the race with a straight cash bid.
Sinclair will become Keegan's third summer signing after the capture of David Seaman from Arsenal and Michael Tarnat from Bayern Munich.
Former Blackpool and QPR star Sinclair handed in a transfer request at West Ham in October 2001 before later withdrawing it.
West Ham were relegated from the Premiership last season.