The 37-year-old has been without a club since departing Championship outfit Blackburn Rovers in June.
Gomes - who also represented Boavista, Fiorentina and Braga - is best known for his time at Portuguese giants Benfica.
During two playing spells at the Estadio da Luz, Gomes scored 166 goals and won seven trophies, including two Primeira Liga titles.
A statement on Benfica's official website read: "At age 37, and after putting an end to his career as a player, Nuno Gomes is back at Benfica, assuming the role of advisor to the president Luis Filipe Vieira for international matters.
"This resulted from the belief, by the club leaders, that he will be of enormous benefit to the club and from Nuno Gomes' desire in returning to the home that he served and made him write some of the most beautiful pages in Portuguese football."
As well as enjoying success at domestic level, Gomes was a regular for the Portugal national team and earned 79 caps, scoring 29 goals.
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