The 28-year-old finalised his move to Eastlands this week following the end of his country's involvement in the World Cup.
The signing is City's second of the week following the capture of David Silva from Valencia and unites Toure with his brother Kolo, the club's captain.
City manager Roberto Mancini told the club's website, www.mcfc.co.uk: "This is another fantastic signing for Manchester City and I am very pleased Yaya has joined us, he is a very good player."
He added: "Everyone knows Yaya is a player that we have admired for a long time and we would like to welcome him to Manchester City.
"He has played at the top level with Barcelona and I am sure his experience and ability will be very important for us."
A fee has not yet been confirmed by the club but reports earlier this week suggested the deal could be worth ¦pound;28million.
That would take the club's spending this summer beyond the ¦pound;60million mark having also completed a ¦pound;10.5million deal for Jerome Boateng from Hamburg.
City, who spent ¦pound;120million last summer, have also been linked with Aston Villa and England midfielder James Milner.
Toure spent three years at the Nou Camp, winning two Spanish titles and the Champions League in 2009.
Toure is expected to join up with his team-mates for their pre-season tour to the United States later this month after enjoying a late break following the World Cup.
Source: PA
Source: PA