The collaboration would cover Areva's 5MW offshore turbine, and would have the two parties working on the development of an 8MW machine.
Significantly, Gamesa's 5MW turbine is not included in the deal. The manufacturer will continue to build the turbine, but it will now be marketed solely for onshore use.
However, the joint venture would work on an "enhanced" 5MW turbine based on Gamesa's technology.
Both companies have previously announced that they are working on machines around the 8MW mark designed for offshore use.
In November, Areva announced plans to build an 8MW turbine, which it expected to prototype in 2015. Serial production is set for 2018.
Gamesa has been planning a 7-8MW turbine since 2010 although most of its efforts have been spent on the 5MW machine.
In October executive chairman Ignacio Galan said the company was working on a 7-8MW, with a prototype due in 2017. Little is known about the turbine, although Gamesa is believed to be looking at using segemented blades.
A spokesperson for Gamesa said that the companies will collaborate on all elements of the new turbine development.
However, Areva will transfer ownership of its turbine assembly plant in Bremerhaven and blade factory in Stade to the venture, as well as offshore wind technology and commercial contracts.
Gamesa will provide its existing multi-megawatt technologies applicable to offshore, as well as offshore-related engineering, operation and maintenance capabilities.
Additionally, the joint venture will enter into a preferred supplier agreement with Gamesa for some "key components".
Areva has already installed 120 of its 5MW turbines in the North Sea, while Gamesa is yet to make a commercial move into offshore wind.
Gamesa's 5MW machine was intended for both offshore and onshore, but will now be confined to dry land. The company made its first sale of the turbine in July for use on a Finnish onshore project.
"By choosing to create a European offshore wind champion with Gamesa, Areva is playing a key role in the consolidation, already underway, of the offshore wind sector," said Luc Oursel, Areva CEO.
In September, Mitsubishi Heavy Industries (MHI) and Vestas formed a joint venture to work together on the development of large offshore turbines.
Both manufacturers also entered the joint venture with machines under development — Vestas' V168-8MW and MHI's 7MW SeaAngel.