The addition of the 100-plus A-League capped Coyne follows the acquisition of Socceroos central defender Michael Beauchamp by the Sky Blues two weeks ago.
Sydney FC coach Vitezslav Lavicka identified Coyne as an experienced, versatile and professional defender who could bolster his defensive options for next season and after Coyne impressed at training and in a friendly match last week he was signed by the two-time A-League Champions.
"I am really happy to have signed for Sydney FC. I have a lot to offer," Coyne said.
"I have played against Sydney FC many times and all I wanted to do was beat them and they were games where you needed no motivation to rip in. Now I will be on the other side and I will be giving it my all.
"I am naturally competitive and I will bring that to Sydney FC. I will play hard and give everything I've got. It is an exciting time for me."