The 29-year-old midfielder won three A-League titles with Brisbane Roar and an FFA Cup with Melbourne City.

As first reported by The World Game, Brattan has signed a one-year deal after moving across from City, who on Friday announced they had signed Uruguayan, Adrian Luna on a two-year deal.

Brattan has joined fellow midfielders Alexander Baumjohann and Anthony Caceres in signing with Sydney, who have also acquired Socceroos central defender Ryan McGowan and New Zealand forward Kosta Barbarouses.

"Luke is a highly experienced player in this league and will strengthen our squad, providing exceptional competition for places," Sydney FC coach Steve Corica said.

"Like many in our squad, he is a winner."

Brattan will begin training with Sydney on Saturday.

He could play in a pre-season game against NPL club St George FC next Tuesday and is set to travel to China for the Sky Blues' match with French glamour side Paris Saint-Germain at the end of the month.

'"We have some fantastic quality in the squad who I am looking forward to playing alongside," Brattan said.

"Sydney FC is the benchmark in the A-League and my aim is to help push that to another level this season.

"I'm looking forward to winning more trophies with this incredible group of players and helping to take this club to our best ever finish in the AFC Champions League."

The 27-year-old Luna has played almost 300 matches in multiple competitions in Uruguay, Spain and Mexico, scoring 38 goals and registering 36 assists.

"Adrian Luna is a creative, attacking midfield player with a proven ability to beat defenders, play key passes and take his chances in front of goal," Melbourne City director of football Michael Petrillo said.

Luna played in the Montevideo Wanderers youth system with fellow City signing, Javier Cabrera and they reunited six years later in Uruguay's Under-20 squad.