Located in New York State, the Nassau County sanitation network covers 1.2 million customers on Long Island.
Upon treating, the wastewater will be disposed into estuaries that are close to beaches and bays.
The local authority will invest more than $830m in the system in the coming years.
The project, which will save Nassau County $230m, will address the damage caused by Hurricane Sandy that devastated a large part of the coast in 2012.
Suez Environnement chief executive officer Jean-Louis Chaussade said: "This agreement marks a new stage for Nassau County, to which we are going to offer all our expertise in order to provide an exemplary service that will satisfy customers and comply with environmental regulations.
"This agreement is also a highlight for SUEZ ENVIRONNEMENT, which is confirming its international expansion and more specifically its operations in North America, following the signing of two sizeable contracts, one for water management in California and one for waste management in Canada in 2014."
