Under the agreement, the Spanish energy firm will be responsible for installing and commissioning the development. It will also construct the electrical substation and power lines.
Spanish turbine manufacturer Gamesa will provide 25 G90 2MW turbines to the project, 140 kilometres south of the capital, Tegucigalpa.
San Marcos is expected to be online in 2015. The country's state utility, Nacional de Energia Electica, signed a power purchase agreement for the development in 2012.
Iberdrola and Gamesa previously worked together on the 102MW Cerro de Hula project in central Honduras. Gamesa supplied 51 G87 2MW turbines to this project.