The La Liga side did not give any financial details but Spanish media estimated the transfer fee at 8.5 million euros (7.24 million pounds).
"Valencia Club de Futbol have reached an agreement with Portuguese international Luis Carlos Almeida -- 'Nani' -- for the player to join the club for the next three seasons," the club said on its website (en.valenciacf.com) on Tuesday.
Valencia had to fend off interest from top-flight English club Stoke City to make the former Manchester United and Sporting player their first signing of the close season.
The 29-year-old, who has scored 20 times in 101 games for his country, was on impressive form last season with eight goals in 28 league games to help the Turkish club finish runners-up.
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Nani won four Premier League titles in an eight-year spell at Old Trafford and joined Fenerbahce last summer on a three-year deal after spending the 2014-15 season on loan at Sporting.
He has started all five games for Portugal at the Euros in France, scoring twice and setting up one goal. He is set to line up alongside Cristiano Ronaldo in attack against Wales in Lyon.
(Editing by Ken Fferris)
