"A new challenge in my career," the attacking midfielder wrote on twitter. "Very happy and proud to have arrived at a great club @SantosFC. A big hello to all the club's fans."
Nine Sporting players quit the Lisbon club last month after an attack in May on a training camp by hooded supporters, some armed with sticks, in which Dutch forward Bas Dost was injured and the dressing room was vandalised.
The incidents came at the end of a tumultuous campaign for Sporting who finished third in the Primeira Liga and reached the quarter-finals of the Europa League.
Sporting members overwhelmingly voted last month to remove president Bruno de Carvalho, whom the nine players had blamed for stoking anger among fans with his public rebuke of the team over their performance last season.
Portugal midfielder Bruno Fernandes rejoined the club on Tuesday, saying he believed it had a more stable future. Fernandes did not rule out that other players may return to Sporting, but said he could only speak for himself.
He has 112 caps and has scored 24 goals for his country.
(Reporting by Andrew Downie; Editing by Ken Ferris)