The Spanish manufacturer will install eight G97-2MW turbines and 17 G117-2MW machines on Exus Management Partners' Pisco project in the Guarda region in the north of the country.
The turbines are due to be delivered in the first half of 2015, with commissioning expected by the end of the year.
This is Gamesa's first contract with Exus, an international investment and asset management company focused on the renewable energy sector. Exus currently has 252MW of wind capacity under management in Spain and Portugal.
Gamesa said that it has installed 438MW in Portugal since it entered the market in 1998.
Portugal had an installed capacity of 4.7GW at the end of 2013, with 200MW coming online last year. Portugal's wind energy association Apren said that it expects a further drop off in installations this year due to a regulatory change in 2013 that cut the feed-in tariff.