The former Chelsea midfielder was scheduled to begin working with the new MLS franchise at the beginning of this month, but has had his loan to Manchester City extended until the end of the current Premier League season.
There has been confusion over Lampard's status in recent days, however, with the Premier League revealing it understands the ex-England international has no existing agreement with the New York side.
But Lampard, whose deal is thought to be with parent company City Football Group, took to Facebook on Friday to clarify his circumstances and declare his excitement about his impending move to the United States.
"I want to make it completely clear about my situation as I have read a lot of lies and nonsense over the last few days," he said.
"When released from Chelsea last year at the end of my contract I signed a commitment to play in NYCFC for two years starting January 1st 2015.
"I was then offered the chance to train and be part of the Man City squad in the interim to keep myself in the best shape going into New York.
"This period has since been extended by Man City and I now will start playing for NYCFC at the end of this current Premier League season.
"There has always been a constant dialogue between all parties in this time to find the best solution for everyone.
"I can say that I am very excited about arriving in New York and giving everything to the team to make us a success in the MLS as soon as possible.
"Thanks everyone for your ongoing support and I wish everyone a healthy and happy 2015."
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