The office will be headed up by Leila Thabet, taking the agency's presence to eight offices across five continents, with an initial North American client roster that includes Adidas and De Beers.
The launch follows the formation of regional hubs in Munich, Sao Paulo and Singapore last year.
Thabet, who will be MD of the New York offering, takes the role after working at We Are Social's UK office, where she worked on accounts for Coca-Cola, Unilever and Tesco.
She said: 'With US-based marketers increasingly responsible for social media strategy and implementation at a global level, we will be able to service these global accounts from New York with support from our international offices.'
Thabet has previously worked as head of social media at Cake.
Robin Grant, global MD at We Are Social, said: 'We've opened up offices in several other places around the world and we figured it was about time for the world's biggest market in what we do.
'The opening of We Are Social New York rounds out We Are Social's global offering. It's something we've not taken lightly, which is why we've opened other offices around the world before this one, but this is the right time for us and we're ready for it.'
Grant added that in the long term an eye was being cast over further possible bases in Asia and North America.