Smokers will no longer be allowed to light up in parks, beaches, public plazas and on boardwalks.
The Bloomberg administration says the ban will protect people from second-hand smoke and help keep parks and beaches clean.
Some health experts questioned whether the smoke poses a serious danger in open, outdoor spaces.
Critics of the law say the city is trampling on civil liberties.
Those who break the law could face fines of $50 per violation.
However, the city has said it plans to rely on signs and social pressure instead of active enforcement.
The expansion comes almost a decade after the city banned smoking in restaurants, bars and other public indoor spaces.