The 35-year-old forward had been strongly linked with the club, who were relegated from the Premier League last season.
Gomes, who was released by Sporting Braga at the end of last season, will join midfielder Danny Murphy and striker Leon Best in signing for Rovers after receiving international clearance.
The striker has agreed a two-year deal at Ewood Park.
Gomes made 79 appearances for his country, scoring 29 times - including seven at major tournaments.
He peaked at international level with four goals at Euro 2000 as his side reached the semi-finals of the competition.
Gomes played for Boavista and Benfica before earning a 17 million euro move to Fiorentina.
He later returned to Benfica and later joined Braga, scoring six times in 20 outings last term.