Mendes seals Sporting switch
The 30-year-old has signed a contract for 2-1/2 years, Sporting added in a statement on their website.
Mendes joined Rangers in 2008 and played 35 games, scoring three goals. He had previously played for English Premier League clubs Portsmouth and Tottenham Hotspur and won the Champions League with Porto in 2004.
The midfielder has won four international caps.