The 36-year-old left Chelsea at the end of last season after 13 seasons and a club record 211 goals.
The midfielder becomes New York City FC's fourth player and second major summer signing following the arrival of David Villa from Atletico Madrid.
Lampard, who has signed a two-year deal with his new club, made 649 appearances for Chelsea since signing from West Ham in 2001
He has played 106 times for England, scoring 29 goals.
He signed a one-year contract extension with the Blues in May 2013 after mulling over a move to Los Angeles Galaxy, who he will now play in opposition from next spring.
New York City FC sporting director Claudio Reyna said Lampard was "one of the greatest players over the last 15 years" and "ticked all the boxes" in terms of a signing.
The move appealed to Lampard, too.
Lampard said at a media conference in New York, streamed live on nycfc.com: "Why not chose New York City? For me talking about it ticking all the boxes, personally for me it does exactly the same.
"It's a very exciting challenge for me in life terms.
"I've seen a real long-term plan and I wanted to be part of that
I want to test myself, I want to carry on challenging myself.
"It was a good time for myself and Chelsea that I moved on."
Lampard did not speak to former England team-mate and ex-LA Galaxy captain David Beckham about MLS.
"I know David pretty well, but we're not on every day speaking terms," Lampard added.
"I've spoken to him about his experiences in the MLS (but) the decision was all mine.
"There's a lot of new challenges here, but I'm coming to a great city and I wanted to show people that I can play good football."
Lampard is still to determine what the immediate future holds, given the season begins in 2015.
He added: "I'm going to keep fit, that's the main thing
How I do that is not clear yet.
"I'm going to sit round with people at the club and sort that out."
Lampard was in England's 23-man squad for the World Cup in Brazil but is still to decide on his international future, prioritising his club future.
"In terms of England, I've had a bit of time after the World Cup which was obviously a huge disappointment," he added.
"I now need to think about England and think about what I want to do next.
"Now I know where I'll be playing my football next year I can make that decision."
Source : PA
Source: PA