The midfielder, who is Chelsea's all-time record goalscorer with 211 goals in 649 matches, has been loaned to the Premier League champions by their MLS sister club, New York City FC. He will play for Manuel Pellegrini's team until the 2015 MLS season kicks off.
Lampard, 36, linked up with his new team-mates on Wednesday and will officially be a City player until January, with the MLS season beginning in March.
He said: "Joining up with Manchester City is a fantastic opportunity for me to continue to train and play at the top level and make sure I am in top condition for New York City.
"It has been an amazing few days for me since the unveiling in Brooklyn and everyone connected with both clubs has been fantastic to me. This is a new chapter of my career and I'm really excited about the experience.
"I met Manuel and some of the players in New York and I'm looking forward to getting into training and making a contribution for Manchester City ahead of my move over to New York."
City have confirmed that Lampard, who represented England at the World Cup finals, is eligible for domestic and European competition and will wear the No. 18 shirt.
"Frank is a world class midfielder and this is an opportunity which works perfectly for everyone, the player, Manchester City, and New York City," said Pellegrini.
"I'm looking forward to working with him and integrating him into our squad. New York have made a fantastic signing by recruiting Frank, and I'm really pleased that we'll be able to have him with us for the first half of our season and help prepare him for his new challenge."
Frank Lampard signe au New-York FC
It's an attention-grabbing signing, but one which will have no real impact on the title race. Lampard's main mission at City is to maintain his fitness for March and it is hard to see where he fits into Manuel Pellegrini's starting XI, particularly with the club having strengthened their midfield already with the signing of Fernando. In other words, don't bother picking Lamps in your fantasy team...
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- Manchester City
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- New York City